One of the Church of England's most senior bishops is warning that people will die unless Muslim leaders in Britain speak out in defence of the right to change faith.

Michael Nazir-Ali, the Bishop of Rochester, whose father converted from Islam to Christianity in Pakistan, says he is looking to Muslim leaders in Britain to 'uphold basic civil liberties, including the right for people to believe what they wish to believe and to even change their beliefs if they wish to do so'.

Some Islamic texts brand Muslims who convert to other faiths as 'apostates' and call for them to be punished. Seven of the world's 57 Islamic states - including Iran - impose the death penalty for conversion.

Now Ali, who some see as a potential Archbishop of Canterbury, has told Channel 4's Dispatches programme of his fears about the safety of the estimated 3,000 Muslims who have converted to other faiths in Britain.

'It is very common in the world today, including in this country, for people who have changed their faith, particularly from being Muslim to being Christian, to be ostracised, to lose their job, for their marriages to be dissolved, for children to be taken away,' Ali said. 'And this is why some leadership is necessary from Muslim leaders themselves to say that this is not what Islam teaches.'

The bishop warns that Muslims who switch faiths in Britain could be killed if the current climate continues. 'We have seen honour killings have happened, and there is no reason why this kind of thing cannot happen.'

In 2004, Prince Charles asked British Muslim leaders to renounce laws of apostasy and the death sentence for converts in Islamic countries, but no public statement was ever made.

Dispatches obtained Islamic texts sold in Britain that say the punishment for apostasy is death - according to all four schools of Islamic jurisprudence. One text called for Muslims to cut off the head of those who reject Islam.

The radical Islamist group Hizb ut-Tahrir, which some in Britain want to see banned, states in its constitution that in countries that practise Sharia law, apostates are to be executed. Its message is disseminated on university campuses across Britain and has found a following among a minority of young Muslims.

A poll of more than 1,000 British Muslims, conducted by the Policy Exchange think-tank this year, found that 36 per cent of Muslims aged between 16 and 24 believe those who convert to another faith should be punished by death.

Sheikh Mogra, a senior member of the Muslim Council for Britain, told Dispatches: 'We live in a country where we respect people's choices. It is not right for any British Muslim to harm in any way whatsoever; to bully them, to intimidate them, to threaten them, is all against Muslim law.'

One convert interviewed for the programme told how his local Muslim community in Bradford closed ranks against him after he switched to Christianity. 'They told me categorically had I been in an Islamic country - Pakistan, Middle East - that they would actually be the first to chop off my head,' he said.

· 'Dispatches: Unholy War' will be on Channel 4 at 8pm tomorrow.