Generally, only include a person's religion if it is relevant to the story.
Church/church: Lower case for the actual buildings; otherwise Church. No human being should be referred to as ‘Head of the Church’. The King is the Supreme Governor of the Church of England. The Pope is the Supreme Pontiff, Chief Pastor or leader of the Roman Catholic Church; he should not be referred to as the ‘Holy Father’, unless you are quoting somebody.
Christmas: Spell in full - do not use Xmas, even for headlines. And remember that not all Christians celebrate Christmas on 25 December. Some Eastern Orthodox Churches mark the festival on 7 January.
The Church of England is not the only Anglican body in the British Isles. There is also the Church in Wales, as well as the Episcopal Church in Scotland, and the Church of Ireland.
Catholicism: Do not automatically equate ‘Catholic’ with ‘Roman Catholic’. There are Catholics who are Anglicans or members of other denominations not in communion with the See of Rome. Always ‘Catholic’, ie with initial cap, in the religious context. Lower case in the sense of ‘catholic taste’, or similar.
Pope: Always use an initial cap for the Pope, whether or not his name is attached. But use lower case in any reference to the pontiff - also when referring to popes in general, or using the terms papal or papacy. Do not refer to the Pope as ‘the Holy Father’ - a term which might offend some non-Catholics.
Vatican: Vatican City is a landlocked city-state situated within Rome. It is administered by the Holy See (the Catholic Church) which has exclusive sovereignty over the country. The Vatican can be used interchangeably in stories when referring to the Roman Catholic Church.
The mainstream groups are Sunni Muslims and Shia Muslims (who should not be described as ‘Shiite’).
Our style for the founder of the faith is the Prophet Muhammad (at second reference, Muhammad or the Prophet).
The Sunnis have no institutional clergy, although each mosque has an imam (often addressed by the honorific Sheikh) who teaches, leads prayers etc. The highest religious authority in a Sunni Muslim country is the mufti, who issues fatwas, or religious edicts. Shia Muslims do have a clergy, whose members are known generically as mullahs. The highest Shia religious authority is an ayatollah.
“Allahu akbar”: is our preferred spelling and the translation should be “God is greatest” rather than “God is great”. Allahu is capped up, akbar capped down.
Burka: is our favoured spelling for this form of Islamic veil, which covers the entire face and body.
Kufr: The Islamic concept of unbelief, of being outside Islam. An unbeliever is a kafir, the plural is kuffar. However, in a direct quote ‘kafirs’ is acceptable.
Koran: Is our spelling of the Islamic sacred book - not Quran or Qur’an.
Islamist v Islamic: The term 'Islamist' has come to refer to those who derive a political course from Islam, so, where appropriate, we can talk in terms of eg: ‘Islamist militants’, ‘extreme Islamists’ or ‘radical Islamist groups’. But specific descriptions are generally better than broad labels.