Speaking in advance of his first Christmas Day sermon as archbishop, he has given a warning that the imprisonment of suspects at Guantanamo Bay, Cuba, and in Belmarsh prison, south London, may be sending out the wrong message.

His sermon is expected to extend a hand of friendship to Britain’s Muslim community. The reference to another faith is a surprising departure in an address by a church leader on the day of an important Christian festival.

His concern over Christian-Muslim relations was reflected by the priority he gave last week to two meetings: with the Iraqi governing council and with the Iranian ambassador.

Before war broke out in Iraq, Williams was outspoken in his opposition to the conflict. He now fears that the intimidation of the Muslim community will have far-reaching consequences.

Referring to the nine British Muslims held in Cuba and the 14 men detained in Belmarsh and in a jail in Buckinghamshire, he said: “These make it harder to encourage and give the right message to those moderate Muslims like our visitors from Iraq, who are very keen to establish constitutional principles of religious toleration in what will clearly be a Muslim state.

“If we want to persuade moderate Muslims to sign up to toleration and pluralism of the right kind, anything that gives the impression that we are targeting Muslims is problematic. We have a lot of ground to make up.”

Pre-empting possible criticism that he may be selling Christians short by taking such a strong interest in another faith, he added: “You can hold out a hand of friendship without in any sense compromising belief or truth. There is theological debate here which is real and deep because we share some history and therefore can discuss it.”

Williams believes westerners find it difficult to grasp that for a Muslim, being religious is not something that is done in addition to everything else: “It just is the fabric. For the Muslim everything is seen through that lens.” Dialogue between Christians and Muslims had been a preoccupation during the past year, he said. During the conflict in Iraq he hosted a three-day seminar in Qatar that brought 30 Christians and Islamic scholars together.

“We sat down to discuss each others’ scriptures, listening to interpretations on both sides,” he said. “We confronted difficult questions such as a Muslim asking me what I mean by Christ being our saviour. We asked them what they understood by the word ‘prophet’. The dialogue showed us that you can have public disagreement and mutual respect.”

It is expected that Williams will also use his Christmas address to make a scathing attack on the French government’s decision to ban Muslim headscarves in schools.

“A number of Christians have said they want to be on side with Muslims in fighting this particular one,” he said.

“The dogmatic secularism of the French government is becoming very provocative and very destructive. The argument in favour of keeping religious symbols is that there is no such thing as a neutral public space in which everybody has to put aside that which makes them distinctive.”

The archbishop fears that a similar emphasis on the secular at the expense of the religious will be promoted through a European constitution.

The Pope has already called for a reference to Christianity to be included in a future European constitution, saying that Christianity is “the religion of Europeans”. This has failed to move the people who are drafting the constitution; no mention of God or Christianity was included in their last draft.

It has been a tough first year for Williams who was enthroned in February. The church has been dogged by its worst outbreak of internecine squabbling since differences over the ordination of women were settled in 1992. Ferocious evangelical opposition to the appointment of Jeffrey John, an openly gay priest, as Bishop of Reading led Williams to persuade him to stand down.

Williams has already sounded a note of despair in a Christmas message that was recently published on the internet. He described the past year as “a time of great uncertainty and disturbance in our Church”.

He wrote: “Before becoming preoccupied with our neighbour’s failings, we must in the presence of the Christ child look first to our own birth and death; to where we see the centre and the edge; to how we find God’s centre, not just the centre of our own concerns and anxieties.”

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