British India's Hindu-Muslim political rift was first institutionalized when the British awarded Muslims separate electorates in the 1909 Minto-Morley awards. Many refer to this decision as the seed of Pakistan.
Later, in 1918, the Montagu Chelmsford Report commented on separate communal electorates - "that they perpetuated class division; that they stereotyped existing relations; that they constituted 'a very serious hindrance to the development of the self-governing principle'".
The Report also said, "A minority which is given special representation owing to its weak and backward state, is positively encouraged to settle down into a feeling of satisfied security; it is under no inducement to educate and qualify itself to make good the ground it has lost compared with the stronger majority. On the other hand, the latter will be tempted to feel that they have done all they need to do for their weaker fellow countrymen and that they are free to use their power for their own purposes. The give-and-take which is the essence of political life is lacking. There is no inducement to one side to forbear, or to the other to exert itself. The communal system stereotypes existing relations."
The Report however said "much as we regret the necessity" the separate electorate system must be maintained "even at the price of slower progress towards the realization of a common citizenship." because "the Muhammadans relied on past assurances which they regarded as vital to their interests, and which the community as a whole protested must not be withdrawn." 
In the Government of India Act 1935, the British government indirectly granted the demand of Muslims that residuary powers be vested in the provinces (not in the future Central Government which would have a majority of Hindus), by vesting residuary powers with the Governor General at his discretion.
Other safeguards included granting non-interference in religious affairs (in common with other religious communities). The Muslim Personal Law Act or the Shariat Act was brought into force in 1937. BR Ambedkar comments on some of these provisions in his book Pakistan or the Partition of India.
By 1937-1939, after formation of elected provincial governments, Jinnah decided that the Communal Award and all other awards were insufficient and that parity for Muslims was the only meaningful safeguard. In 1940 Jinnah said "So far as I have understood Islam, it does not advocate a democracy which would allow the majority of non-Muslims to decide the fate of the Muslims". In 1940 he also spoke of how the Muslims constituted not a mere minority, but a nation and must have their own homeland.
BR. Ambedkar says of this period " In 1929, the Muslims insisted that in allotting seats in Legislatures, a majority shall not be reduced to a minority or equality. This principle, enunciated by themselves, it is now demanded, shall be abandoned and a majority shall be reduced to equality. The Muslims in 1929 admitted that the other minorities required protection and that they must have it in the same manner as the Muslims. The only distinction made between the Muslims and other minorities was as to the extent of the protection. The Muslims claimed a higher degree of protection than was conceded to the other minorities on the ground of their political importance. The necessity and adequacy of protection for the other minorities the Muslims never denied. But with this new demand of 50 per cent. the Muslims are not only seeking to reduce the Hindu majority to a minority but they are also cutting into the political rights of the other minorities." 
With the demand for parity, Muslim demands for safeguards as a minority crossed the bounds of natural justice and became undisguised power politics. Hindu-Muslim politics was now at the point of no return and the British had either engineered or encouraged this to happen. Despite Muslim League winning only four and a half percent of the Muslim vote in 1937, Jinnah's claim to speak for the entire Muslim community was accepted in 1939-40 by the British. who wanted leverage against the Congress movement at a time when W.W.II had begun and the Congress was refusing to cooperate in the war effort. 
In 1946, during the discussions with the Cabinet Mission, Jinnah made it clear he wanted a sovereign Pakistan consisting of six provinces. If he was to concede a Union between a virtually sovereign Pakistan and Hindustan, it would be as a trial for 5 to 10 years and there must be parity between Muslims and non Muslims, and between Hindu majority provinces and Muslim majority provinces.
He was against proportional representation in any future Union legislature or Union government. He was opposed to the Union Centre having a legislature at all and to the Union Centre having any executive or financial power other than over those defence and foreign policy matters on which federating units, Hindustan and Pakistan, could both agree upon.
The compulsory grouping scheme would give Jinnah the power to obtain all the concessions he wanted from the Congress/Section A majority at Union level while retaining the option of breaking off a sovereign Pakistan composed of Sections B and C. His Pakistan would then have included most of present-day Indian Punjab, Haryana (extending to the outskirts of Delhi), sections of Himachal Pradesh, all of West Bengal and all of the North-East.
The parity which Jinnah sought as safeguard was in fact a Pakistani veto over Hindustanis of all religions/regions. Jinnah perhaps felt that such a veto within an Indian Union would give more power to Muslims of Muslim majority provinces than a separate sovereign state, which was an option which he and the Muslim League clearly stated they were not giving up even in their acceptance of the Cabinet Mission Plan.
But the Congress, however powerful an organization in itself, had no mandate to sign away the fundamental rights of those Indians whom it claimed to represent and to hand Jinnah and the Muslim League an artificial parity with Hindustan/India and a veto over its affairs (and Congress's plans) for the sake of an illusory unity on the League's terms. The Congress preferred to let the Muslim League have a sovereign state with the non Muslim majority parts removed and to receive its own sovereign state sans League interference.
In short, Jinnah's acceptance of the Cabinet Mission Plan did not denote his acceptance of a united India, it denoted his and the Muslim League's opting for a larger Pakistan after the British left. The Congress refusal to yield on the compulsory grouping scheme of the Mission Plan was a rejection of a larger Pakistan at a later time and rejection of a Pakistani veto over India and its constitution until that time.
In the years preceding, Jinnah had been successful in using his opposition to the Congress as leverage to get concessions from the British and then leveraging his clout with the British to get concessions from the Congress. Jinnah believed that if his terms were not agreed to by the Congress, this time too, his terms would be forced on them by the British, as had happened before.
The British Government and the Cabinet Mission broadly supported Jinnah's claims for equality/parity and their (and the Muslim League's) inflexibility on the compulsory groupings scheme/Sections followed from that( Wavell said it was meant to deal with a 'psychological difficulty').
The Cabinet Mission and later the British Government refused to reconsider the compulsory groupings scheme in spite of its long term un-sustainability, in spite of unrelenting Congress opposition to it, and in spite of the fact that the scheme did not take into account issues like Assam's non Muslim majority and the sidelining of Sikh concerns. (It would be interesting to study if similarly unsustainable constitutional contraptions were imposed by the British on the Middle East, and lie at the root of some of the troubles there.)
The British Government tried to pressurize the Congress into accepting the Cabinet Mission Plan's compulsory grouping scheme without any changes, including by attempting to postpone the meeting of the Constituent Assembly whose first meeting finally took place in December 1946.
But the British were not in fact, in a position to impose any solution on the Congress. The British were also unwilling to stay on in India until such a time as they could impose a constitutional solution of their choice partly because of the steadily deteriorating situation including communal riots, mutinies in the Armed Forces and general civic breakdown.
So Jinnah was left protesting Congress's refusal to accept the Cabinet Mission's terms to the letter. He was left protesting the meeting of the Constituent Assembly. He was left demanding that its very existence, the resolutions it passed and activities towards writing a constitution be declared null and void by the British. His pleas did not work because the British could do nothing to stop the Congress from making progress on an Indian Constitution which the country was awaiting in anticipation of full independence after a long struggle.
It is interesting that Jinnah did not call a Constituent Assembly sitting of his own with willing Muslims Leaguers as participants and that he contented himself with protesting what the Congress did. Today, 58 years later Pakistan is still discussing what its constitution should be.
It is also interesting that successive Pakistani leaders have projected imposed parity between disparate and disproportionately sized population groups or outright minority rule, as being key to the success of Pakistani nationalism and governance. 'One man one vote' has been generally considered much less relevant to the issue.
Having a sovereign state Pakistan with full independence was, in my opinion, a better option for a majority of Indian Muslims in preference to remaining a minority within united India. But Pakistan's founding fathers were so imbued with the politics of rancor against India that they failed to realize that in giving up all say in India's affairs by becoming a separate state and simultaneously choosing to foster enmity with India, they willfully created a dangerous situation for Pakistan. The Kashmir war served to set the seal on a future course of conflict.
Jinnah might have expected the British to intercede in Pakistan's favor in the Kashmir War. Pakistan's stance with respect to India has not changed since the time Jinnah first offered up his usefulness to the British. Pakistan still considers parity with India to be a basic requirement for its security and expects the US, the successor power to the British, to provide it such leverage. But the US is not in any better position to do so than the British were, I think.
My concluding (and starting) point is that Constitutional/political parity between Hindus and Muslims, or between Hindustan and Pakistan as Jinnah demanded as the price for a united India was an unsustainable option. Even had every last four-anna Congress member signed off on it, such parity would not have been digestible by the general public and would have led to political chaos. As the forced basis for collective decision making, it would have led to failure to write a constitution for India.
Eventual civil war could also have ensued since the British Indian Army was heavily weighted with the North Western region's minority which was seeking to rein in the political rights of the majority (similar to what happened in East Pakistan in 1971).
Jinnah's demand that the Indian Army be first split up on basis of a sovereign Pakistan and the two-nation theory and then be reconstituted for a united India's defence was also unworkable - as BR Ambedkar remarked(), the two nation theory was a dangerous basis for a united Indian Army.
'Universal franchise and joint electorates', a fundamental element of the Congress's vision of nationalism would have had to compete with 'Parity', a fundamental element of Muslim League's vision of nationalism, as the central nonnegotiable element of united Indian nationalism.
Forced parity between the disproportionate populations of Hindustan and Pakistan or forced parity between 25% Muslims and 75% non Muslims would have led to collapse of the Constitution after the first exercise of universal franchise brought home to Indians the true significance of their individual sovereign rights.
Without an emphasis on universal adult franchise, India would have become a Pakistan, a state without a stable constitution or effective functioning legislatures, ruled primarily as a military or civilian dictatorship by a select group of oligarchs claiming sole guardianship of the holy grail of nationalism with provinces having to seek just rights for their citizens via bloody civil war.
History was moving towards one-man one-vote and the political sovereignty of the individual and Muslim League and Pakistan missed the bus. I am thankful that the Congress had the good sense not to submit to the Cabinet Mission Plan. It is solely and wholly due to the Congress that my voting rights are not held hostage to the insecurities and megalomania of Pakistani ruling elites. I am also grateful for the opportunity to have a composite Indian identity (transcending a purely religious/regional one) which resulted from Congress's efforts to uphold inclusive nationalism, however imperfectly. But if any of my Muslim fellow countrymen are unable to make similar categorical statements, I do indeed understand.
Jinnah's two-nation theory formulation and refusal to agree to even a single Congress Muslim member in the Central or provincial government were meant to force Congress to abandon its attempts to represent ANY Muslim point of view. He succeeded to the extent that the preceding 50-odd years of the Indian freedom struggle which the Congress spent attempting to construct a composite nationalism and strategising, organizing or lying in jail resisting the British, were reduced by Jinnah to being worth nothing more than preventing Hindu-majority areas from going to Pakistan in 1946-47.
The only alternative the Congress had to such dismal failure, was to agree to Jinnah's demands for Hindu-Muslim parity, to abandon its Muslim supporters and henceforth continue to fail in the following years until Pakistan finally decided to secede. In other words, the Congress's attempt to practice mass politics which spanned religious boundaries was a decisive failure.
This failure and the 1938 fiasco of its Muslim mass contact program [1o]) might explain Congress's strategy of courting reactionary Muslim leaders and not the Muslim population base after independence.
Before 1937, Muslim politicians made sense (to me)- they were Indians who wanted safeguards as Muslims against Hindu majority rule. After Jinnah, the two nation theory formulation and demand for parity took centre-stage after 1937-38, many Muslim politicians became Pakistanis and stopped making sense. They became demagogues using religion to rouse Muslims' ire against the whole world, the British, and most of all Hindus with whom any compromise was equivalent to accepting slavery and defeat. The mere implicit or explicit assertion of the Hindu numerical majority or disagreement with League's/Jinnah's point of view was deemed equivalent to harbouring an intention to wipe out a hundred million Indian Muslims. 'La ilaha ilallah' became the eternal third rail of subcontinental Muslim politics for which the Congress had and still has no answer. (It appears to have no answer for the sloganeering of Hindu demagogues either).
The question remains, after such abysmal failure in the past, what lies in the future for mass-based politics spanning religious boundaries in India.
Also, the proof of the pudding is in the eating. If India is not able to assure its citizens of any religion, community or region of the very basics of security of life and property and equal opportunities for progress, then all this history becomes moot.
Speech at Lahore Session of the All India Muslim League, March 22, 1940,'Speeches and Documents on the Indian Constitution 1921-47',Vol II, Gwyer and Appadorai, 1957
 Durga Das wrote in 'India from Curzon to Nehru and After', 1969, "The India Office and the Viceroy were now agreed on building up Jinnah as their Crescent Card to neutralise the Congress challenge. This was manifest from Sikander Hayat Khan's disclosure to me that the Viceroy, on instructions from the Secretary of State, had enjoined upon him and Fazlul Haque[of Bengal] not to undermine Jinnah's position as "leader of the Muslim community.". This happened towards the end of 1939, when Jinnah had taken up an uncompromising attitude and the Muslim Premiers of Punjab and Bengal were under pressure from some of their followers "to disown Jinnah or cut him down to size.""
These concessions from the British included acceptance of Jinnah as sole spokesman of Muslims in 1939-40, granting of veto power over India's future constitutional development by Viceroy Linlithgow in 1940, offers of parity in Executive Council in 1945.
Ayesha Jalal, Sole Spokesman-Jinnah, the Muslim League and the Demand for Pakistan, pg193
Last edited for content 5 June 2005. Links updated July 2009
CMP(1) - From Ayesha Jalal's 'The Sole Spokesman'
CMP(2) - Congress and Muslim League positions on 12 May 1946
CMP(3) - The Cabinet Mission Plan 16 May 1946
CMP(4) - Jinnah and ML responses to the CMP 22 May and June 6 1946
CMP(5) - Jinnah's meeting with Mission Delegation on 4 April 1946
CMP(6) - Jinnah's meeting with Missiion Delegation on 16 April 1946
CMP(7A) - Maulana Azad's meeting with Mission Delegation on 17 April 1946
CMP(7) - The Congress unease with parity 8-9 May 1946
CMP(7B) - Jinnah and Azad responses to preliminary proposals 8-9 May 1946
CMP(8A) - Simla Conference meetings on 5 May 1946 on the powers of the Union
CMP(8) - More exchanges on parity, Simla Conference meeting 11 May 1946
CMP(9) - Jinnah and Wyatt(1) on Pakistan and CMP, 8 Jan. and 25 May 1946
CMP(10) - Jinnah and Wyatt(2) on the interim government, 11 June 1946
CMP(11) - Congress opposition to grouping. Gandhi, Patel and Azad, May 1946
CMP(12) - Congress Working Committee resolutions, May-June 1946
CMP(12A) - Arguments over inclusion of a Congress Muslim, June 1946
CMP(12B) - Behind the scenes-Gandhi, June-July 1946
CMP(12C) - Behind the scenes-Jinnah, June-July 1946
CMP(13) - Jawaharlal Nehru's press conference on the Plan, 10 July 1946
CMP(14) - League rejected Plan, called Direct Action, July-August 1946
CMP(15) - Viceroy strong-arming Nehru, Gandhi on compulsory grouping, Pethick-Lawrence to Attlee, Aug -Sept 1946
CMP(16) - Intelligence assessment on Jinnah's options and threat of civil war, Sept. 1946
CMP(17) - League Boycott of the Constituent Assembly Dec. 1946
CMP(17A) - Congress "climbdown" on grouping and Jinnah's rejection, January 1947
CMP (A1) - Plain speaking from Sir Khizr Hayat, Abell on the Breakdown plan, Wavell
CMP(A2) - North West Frontier Province, Oct-Nov 1946 and Feb-March 1947
CMP(A3) - Bengal and Bihar, August - November 1946
CMP(A4) - Punjab, February - March 1947
CMP (18) - My take
CMP (19) - What did parity and communal veto mean in numbers?
CMP(20) - Another take -with links to reference material
CMP(21) - Mountbatten discussing CMP with Patel and Jinnah, 24-26 Apr 1947
CMP(22) - A reply on the Cabinet Mission Plan
Extra(1) - Jinnah's speech in March 1941 on independent sovereign Pakistan
Extra(1A) - Jinnah's Speeches and Statements from 1941-1942
Extra(1B) - Jinnah's Speeches and Statements from 1938-1940
Extra(1C) - Jinnah's speeches and Statements from 1943-45
Extra(2) - Gandhi-Jinnah talks in 1944 on defining Pakistan
Extra(3) - BR Ambedkar quoted from his book 'Pakistan or the Partition of India'
Extra(4) - Congress and Muslim parties' on the Communal question 1927-1931
Extra(4A) - Excerpts of Motilal Nehru Committee Report 1928
Extra(4B) - Nehru, Bose, Jinnah Correspondence 1937-38
Extra(5) - BR Ambedkar on Communal Representation 1909-1947
Extra(6) - Gandhiji's scheme of offering the Prime Ministership to Jinnah in 1947
Extra(6A) - Jinnah on Congress's offers of Prime Ministership 1940-43
Extra (6B) - Apr-Jul 1947 Negotiations on Pakistan between Mountbatten and Jinnah
Extra(7) - M.A.Jinnah and Maulana Azad on two nation theory
Extra(8) - On Separate electorates, Joint electorates and Reserved constituencies
Extra(9) - Links to cartoons on Indian constitutional parleys from the Daily Mail, UK, 1942 and 1946-1947, by L.G. Illingworth
Extra(10) -Nehru Report 1928 (10 MB pdf)
Extra(11) -Iqbal's letters to Jinnah, May-June 1937
Extra(12) -Jinnah, Linlithgow, Sikander Hayat, Pakistan rumblings 1942-43
Durga Das (1) 1919-1931, Jallianwala Bagh to Bhagat Singh
Durga Das (2) 1931-1936, Crescent Card: Jinnah in London to Fazli Husain in Punjab
Durga Das(3) 1937-1940, Provincial Autonomy to Jinnah gets the veto
Durga Das(4) 1940-1945, The War Years: India's War Effort-Pakistan on a platter
Durga Das(5) 1945-1947, The Cabinet Mission to Divide and Quit
1937-1940(2) Congress and Jinnah fall out in U.P., Jinnah's anti-Congress campaign and the Viceroy gives Jinnah a Veto: Ayesha Jalal, Sarvepalli Gopal and Stanley Wolpert
1937: Congress-Jinnah tussle over coalition government in U. P., M.J. Akbar
1937: Nehru, Jinnah and Coalition Governments, Bimal Prasad
1939-1940: India and the War, Anita Inder Singh
1945-1946: The Elections of 1945-46, Anita Inder Singh
1857-1938 Glimpses of British policy in Punjab: Ian Talbot and David Page
1930-1939 Congress Decline in Bengal, John Gallagher
Glendevon (1) 1937: Congress's Office Acceptance Saga over Governor's Powers
Glendevon (2) 1937-1940: Federation, Jinnah, Congress activism in Princely States
Glendevon (3) 1939-1942: Linlithgow, Congress, Jinnah,War-time Realignments
1939-1947: Jinnah and the Anglo-Muslim League Alliance, Narendra Singh Sarila
1944: Gandhi-Jinnah talks, Jaswant Singh
1899-1947: British Forward Policy(2)