The Government signalled yesterday that ministers were prepared to back tough action by Iraq's interim administration against both its former rulers and the insurgents seeking to destabilise the country.

Prime Minister Tony Blair told the Commons that Britain and the US were determined to help the new Iraqi authorities to defeat those "killing as many innocent people as they can, trying to destroy oil and power supplies and create chaos".

Foreign Secretary Jack Straw said that while Britain in principle opposes the use of the death penalty, it was a matter for the Iraqi authorities to determine whether it might be applied to Saddam Hussein and his colleagues who are expected to appear in court today.

In London, some of the gloss was taken off that that symbolic event by a letter from the archbishops and bishops of the Church of England which warned Mr Blair that mistreatment of Iraqi detainees by coalition forces had "deeply damaged" the West in the eyes of Muslims.

In their letter, drawn up following a meeting in Liverpool of all 110 archbishops and bishops this month, the Archbishop of Canterbury, Dr Rowan Williams, and Archbishop of York, Dr David Hope, warned Mr Blair that the credibility of Western governments throughout the Muslim world was undermined by reports of abuse.

They wrote: "It is clear that the apparent breach of international law in relation to the treatment of Iraqi detainees has been deeply damaging.

"The appearance of double standards inevitably diminishes the credibility of Western governments with the people of Iraq and of the Islamic world more generally.

"More fundamentally still, there is a wider risk to our own integrity if we no longer experience a sense of moral shock at the enormity of what appears to have been inflicted on those who were in the custody of western forces."

The letter followed the publication of photographs showing mistreatment of detainees by US troops.