The Archbishop of Canterbury spoke powerfully today of how Christ's victory on the Cross overcame evil.

He called for a memorial for those killed in the London terror attack, in particular to PC Keith Palmer.

Archbishop Justin Welby said the best memorial would be a country that could live together in peace and harmony.

But there also needed to be a physical memorial to those murdered.

'There needs to be a memorial because remembering helps us not repeat. But the best memorial we can build is a country at peace with each other and at peace with itself,' he said at a prayer vigil at Westminster Abbey with leaders representing Christianity, Judaism and Islam.

Archbishop Welby was in Lambeth Palace when he heard the news.

'My first thoughts were prayer and pain for those who were suffering. I'm a Christian. I believe in Christ who died on the Cross and rose from the dead, and in that resurrection demonstrated the triumph of love and self sacrifice over evil and despair and desperation,' he told Christian Today.

Archbishop Welby led the faith leaders in a minute's silence, just yards from where Khalid Masood mowed down pedestrians with his car and murdered PC Keith Palmer on Wednesday.

He said: 'Two days after the attacks across the road behind us, we are still all of us deeply shocked by what has happened, and beginning the process of thinking about the consequences and the future, quite rightly.

'As we come together today a number of people are particularly in our minds. Those who were killed, especially PC Keith Palmer, their families, the police whose consistent courage and observance of duty is an extraordindary example to all of us. Those who are waiting at hospitals and bedsides and praying or hoping or seeking to comfort one another. Also the wider community wondering what this event means as a sign for our future.'

He described it is a moment of sad reflection 'but also a moment of determination for our naton together'. In standing there together, the three Abrahamic faith communities were showing their deep commitment to a peaceful future.

He said Islam, Judaism and Christianity hold together the Psalms.

He quoted Psalm 42: 'Why are you so heavy my soul, why are you cast down? Put your trust in God.' 

In the stories that Christians believe of the death and resurrection of Jesus, there is to be found God who conquers the despair and destruction that these events speak of, he said. 

With him were Chief Rabbi Ephriam Mirvis, Sheikh Ezzat Khalifa, Head Imam of the London Central Mosque, the Shia leader Sheikh Mohammad al Hilli and Cardinal Vincent Nichols, Archbishop of Westminster.

'As Christians what we do is take anger and worry and bring it to Christ in prayer. What we don't do is turn against other people who we know are innocent of anything to do with this event.'

WATCH: The faith leaders talk and pray about  the London terror attack.

WATCH: The Archbishop of Canterbury talk about what he was doing when the attack happened, and how Christians can still have faith.