In a sermon preached in York Minster and attended by members and officers of the Church of England's General Synod who are meeting in York, Dr Williams said the pain of last July's terror attacks in London was still felt deeply:

"Today it is inevitable that we should have much in our minds all those whose lives were so brutally taken away, as well as those whose lives were shattered by injury or bereavement. People of faith have had to try and come to terms with the horrible fact that there are those who want to serve their God and their idea of justice by organised slaughter and suicide."

Dr Williams said those who have used religion to justify terrorist killing promote a blasphemy:

"For the person who resorts to random killing in order to promote the honour of God or the supposed cause of justice it is clear that God is too weak to be trusted. God is too weak to look after his own honour and we are the strong ones who must step in to help him. Such is the underlying blasphemy at work."

People of faith, he said, need to show confidence and trust in God.

"What we need is people in all our communities of such faith that they do not seek to fill the void in their souls by feverish language and action that is blind to the reality of others. It is people who are extreme in their confidence in God who will most effectively challenge the extremists of murder and fear."

Christians, he reminded the congregation, have the example of Jesus' teaching in the gospels to "take nothing for the journey".

"For us to go on our way with nothing in the way of securities for the future is our most eloquent witness to the Lordship of Jesus."