"You, the Queen, should be ashamed!"

By David Smith, The Observer

The slavery bicentenary service was about 45 minutes old and running as smoothly and sombrely as any usual major national commemoration at Westminster Abbey: the singing of hymns, readings from the Bible and an air of inviolable solemnity.

All this was shattered when, from behind my seat in Poets' Corner, a man strode rapidly into the space in front of the altar and began screaming at the top of his voice. The Queen, Prince Philip, Tony and Cherie Blair, John and Pauline Prescott, Gordon and Sarah Brown and the Archbishop of Canterbury watched in stunned disbelief. The bright-shirted black demonstrator, Toyin Agbetu of the African rights organisation Ligali, was only a dozen feet from all of them, with apparently no security guards to block him.

The Archbishop had just delivered his main address and the service had moved on to "confession and absolution". But the reading was stopped in its tracks by Mr Agbetu's outburst: "You should be ashamed. We should not be here. This is an insult to us. I want all the Christians who are Africans to walk out of here with me!"

In a deeply worrying sign in this supposedly terrorist-conscious era, the security guards near my seat were so utterly surprised that they only looked at each other, uncertain whether to intervene. Finally, they did. Seven guards and two ushers gathered around Mr Agbetu and a hand was placed on his arm.

"Let go of me!" he yelled, raising his arms like a suspect confronted by armed police. "I have no weapon! I have no weapon!"

The Queen, on a raised platform and out of Mr Agbetu's immediate reach, watched with pursed lips. The Duke of Edinburgh frowned. Neither seemed frightened for their safety. In the pews, Mr Blair watched with dismay as if already preparing a speech about this "regrettable incident". Mr Brown, whose eyes had been sleepy, was jolted awake. Kwame Kwei-Armah, the actor and writer, dressed in a glittering golden African robe, watched with sorrow in his eyes.

The more that the security men tried to manhandle Mr Agbetu, the more he resisted. Suddenly the interruption turned serious. There were pushes and shoves, even punches. Twice Agbetu and several bodies went crashing into the knees of appalled guests, who were wearing their smartest suits and dresses. All the while Mr Agbetu's bellowing was drowning out the now superfluous service, which had tried to resume.

By now many guests and journalists around me were on their feet, straining to look. There was a sense of danger and drama. It was clear Mr Agbetu would not go quietly. Possibly not without a fight.

After what seemed an eternity, Mr Agbetu was shuffled towards the quire, in the direction of the exit. But he pointed at the Queen and yelled: "You, the Queen, should be ashamed!" The monarch did her national duty by remaining icy calm.

Mr Agbetu was now directly beneath the prime minister. He turned to face him and Mr Blair glared back. The thousands of guests watched in hushed anticipation, wondering what would come next, wondering if Mr Agbetu might even leap on him. Instead the protester screamed: "You should say sorry!"

Mr Agbetu continued walking and shuffling, still resisting the hands being placed on him, still shouting his dissent. Hundreds more guests in the nave got to witness the spectacle. The abbey's ushers still looked unsure quite how to handle him. Finally, outside the building, Mr Agbetu was not bundled away as might be expected. Instead, he gave an impromptu press conference.

"I had always planned to make this demonstration," he said. "The Queen has to say sorry. It was Elizabeth I. She commanded John Hawkins to take his ship. The monarch and the government and the church are all in there patting themselves on the back."

Finally, two police officers took him away for questioning. The service continued to the end but the sepulchral calm had gone. When the guests emerged they were not talking about William Wilberforce.