The Archbishop of York, Dr John Sentamu, has said that Prime Minister Tony Blair should "go a bit further" and make a formal apology for the slave trade on behalf of Britain.

The call came ahead of a ceremony in Ghana to mark the 200th anniversary of the abolition of the slave trade on Sunday, in which the UK's first black cabinet minister Baroness Amos, leader of the House of Lords and a descendent of slaves, will say that slavery was "one of the most shameful and uncomfortable chapters in British history".

Mr Blair, who will address the ceremony in Ghana via video link, expressed earlier in the month "deep sorrow" for the slave trade, saying, "We are sorry."

Dr Sentamu said in an interview with the BBC, however, that Mr Blair needs to go further and make a full apology.

"A nation of this quality should have the sense of saying we are very sorry and we have to put the record straight," he said.

Dr Sentamu joined the Archbishop of Canterbury and other church leaders as they walked through London on Saturday in reflection and repentance for the complicity of the church in the slave trade.

The Archbishop of Canterbury challenged Christians to open their eyes and "see" where people might still be in slavery today, calling on Christians to be "agents of release" and "people committed to freedom".

"By God's grace and the work of some extraordinary human beings 200 years ago, people began to see. It took a long time - an embarrassingly long time," said Dr Williams.