A lone protester has interrupted a commemorative service at Westminster Abbey marking the 200th anniversary of the act to abolish the slave trade.
Toyin Agbetu condemned Africans for taking part in the service
The event, attended by the Queen and Tony Blair, was almost over when human rights campaigner Toyin Agbetu began shouting: "This is an insult to us."
He condemned African Christians for taking part and told them to walk out.
The service resumed minutes later after security guards led him outside. He was arrested and is being held in custody.
Mr Agbetu, 39 - a campaigner for Ligali, an African-British human rights organisation - did have a valid ticket for the service, according to the abbey.
"He came through security checks, the scanners. I'm convinced we did everything correctly," said Maj Gen David Burden, the abbey's receiver-general.
In such cases they would let the man speak before leading him out, he said. "It was not the place to manhandle someone," he added.
Once outside, Mr Agbetu spoke briefly to the media, saying the Queen should say sorry for her ancestors, before police detained him for a public order offence.
"The monarch and the Government and the church are all in there patting themselves on the back," he said.
The event was held to commemorate the Abolition of the Slave Trade Act which became law in March 1807.
The brief disturbance came just ahead of a minute's silence that was followed by the sounding of horns traditionally used to warn of slave trader raids.
Earlier, the Archbishop of Canterbury, Rowan Williams, described slavery as an offence to human dignity and freedom and "the greatest cause of grief to God's spirit".
Dr Williams told the congregation that slavery was not a regional problem in the world, but was "hideously persistent" in our nations and cultures.
"We, who are the heirs of the slave-owning and slave-trading nations of the past, have to face the fact that our historic prosperity was built in large part on this atrocity," he said.
The Queen was among those attending the service
"Those who are the heirs of the communities ravaged by the slave trade know very well that much of their present suffering and struggling is the result of centuries of abuse."
Lady (Kate) Davson, the great-great-great grand-daughter of William Wilberforce, who led the abolition movement, read a House of Commons speech made by her ancestor.
Later the Queen laid flowers on his memorial and the Innocent Victims' Memorial, in honour of all those affected by slavery.
To conclude the national service, all 10 bells at the abbey rang out, with 200 tolls of the tenor bell to mark the 200th anniversary of the Act of Parliament.
'Sorrow and regret'
Linda Ali, of the United Society for the Propagation of the Gospel, said the day was about returning dignity to the slaves and acknowledging their contribution to the British economy.
She also called on Tony Blair who has expressed "deep sorrow and regret" at Britain's role in the slave trade, to go a step further.
"I don't see what is so very difficult about apologising for what is such a great crime against humanity," said Ms Ali.
Lady Davson said she too thought Mr Blair should apologise.
"Slavery is one of the largest pieces of our wounded history, our worldwide wounded history, and...[has] to be confronted in order to get peace in our world."
The prime minister did not speak at the service. His deputy, John Prescott, unveiled a restored memorial fountain to anti-slavery campaigner Thomas Fowell Buxton at Victoria Tower Gardens in London.
Chancellor Gordon Brown, London Mayor Ken Livingstone, Home Secretary John Reid and Culture Secretary Tessa Jowell also attended the event.