Parliament's influence over legislation

While parliamentary rebellions have become more common in recent years, defeats for government measures are rare. Blair did not lose a vote in the Commons until after the 2005 election, when his majority dropped by 100 seats, and even then it took a combination of Labour rebels and the opposition parties to defeat his plans to extend the detention of terrorist suspects to 90 days. More commonly, a government that fears defeat will withdraw a contentious measure.

The size, or absence, of a majority for the governing party in the House of Commons is an important factor in the relationship between the legislature and executive. The first-past-the-post (FPTP) electoral system often, but not always, delivers a working majority for the party that wins most votes in a general election. A government with a large majority is in a commanding position, able to push its legislation through parliament by utilising the whip system and controlling the parliamentary timetable. The larger a government’s majority, the less likely it is that the other parties in the Commons will be able to defeat or amend government bills.

The ability of backbenchers to influence policy is also limited because a government with a substantial majority can absorb dissent within its own ranks. With a majority of 167 at the 2001 election, the Blair government survived large rebellions from Labour backbenchers on Iraq, tuition fees and foundation hospitals. The government suffered its first Commons defeat within months of its majority being cut to 65 at the 2005 election. A governing party that has a slender majority, or none at all, can find itself in a precarious position. A hung parliament occurs when no single party commands an absolute majority of seats in the House of Commons.

Since 2010 there has not been a dominant government majority in the Commons until 2019. This was partly due to the emergence of a multi-party system, with the SNP, in particular, emerging as a major force. If this persists (it may not), the fragmented nature of Parliament makes it harder for the government to control MPs in general. This is especially true, given the persistent split in the Conservative Party.

In recent years Parliament has insisted on taking over control of UK military intervention abroad. This is largely a legacy of the failed policy in Iraq after 2003. Since then Parliament has demanded that it approves major military adventures and directs military policy. For example, Parliament has been directing the nature of UK intervention in the Syrian civil war.

In 2025, the Labour government led by Keir Starmer with a majority of 148, had to make major changes to its welfare reform plans after 120 Labour MPs signaled they would back amendments opposing the government’s proposals.

Concessions on Eligibility: The most significant concession was that the tougher new eligibility rules for Personal Independence Payment (PIP) and the freezing of the Universal Credit health component would only apply to new claimants, not existing ones.
Wider Review: The government agreed to complete a wider review of the welfare system, co-designed with disabled people's organisations, before implementing changes to the PIP assessment criteria.
Reduced Savings: The concessions drastically reduced the estimated annual savings from the reforms by 2030, from an initial goal of around £5bn to approximately £2bn or less.
Bill Passed: Despite the watering down of the bill and a substantial number of Labour MPs voting against it (around 49 in the final vote), the legislation passed the House of Commons due to the government's large majority and some rebels being won over by the concessions.

The events were seen as a blow to Prime Minister Keir Starmer's authority and led to criticism from opposition parties and some within his own party.

Case study: Welfare Rebellion and Labour 2025 The limits of a PM's power

The House of Lords has become increasingly active and obstructive since 1999. Measures which are not subject to the Salisbury Convention are vulnerable to problems in their passage through the Lords. The Lords has become increasingly willing to oppose government measures since the removal of most hereditary peers and the ending of single-party control in the upper house. It has used its power of amendment to secure compromises from the government, as with the 'sunset clause' in the 2005 Prevention of Terrorism Act, but as the unelected chamber it will normally defer to the Commons after making its point. The Parliament Act was used three times by the Blair government to push legislation through

Major Legislative Defeats

Theresa May’s Brexit Deal (2019): On January 15, 2019, the UK Parliament rejected the Government's EU withdrawal agreement by 230 votes (432 to 202). This is the largest defeat for any government in British history.
Margaret Thatcher’s Shops Bill (1986): A rare defeat at the second reading stage occurred when Thatcher’s attempt to liberalize Sunday trading was defeated by 14 votes, despite her having a majority of over 140.
Tony Blair’s Terrorism Bill (2005): Blair’s government was defeated for the first time in eight years when a proposal to hold terror suspects for up to 90 days without charge was rejected by 31 votes.
David Cameron’s Syria Intervention (2013): A motion that would have provisionally authorized military action in Syria was defeated by 13 votes (285 to 272), marking a major shift in the use of royal prerogative for war.