White roses were laid at London's 9/11 memorial garden yesterday, as a small but vocal protest by Islamist extremists failed to disrupt Britain's remembrance of those who died a decade ago.

Some 100 protesters from Muslims Against Crusades gathered at the edge of Grosvenor Square, near the US embassy, to burn an American flag. Using a loudspeaker to proclaim 9/11 as a "great victory", they left shortly before the ceremony. Several glass bottles were thrown as they clashed briefly with a small group of supporters of the far-right English Defence League.

Two men, believed to be EDL members, were stabbed two hours later during an impromptu march by the group along Edgeware Road. Police said eleven people were arrested in connection with the attack.

The ceremony continued unhindered, as the Prince of Wales and the Prime Minister joined relatives of the 67 Britons who died in the attacks. The Prince spoke of the "continuing, awful agony" suffered by the bereaved but said that he hoped for the "healing the world so desperately needs".

Earlier in the same square there was a low-key serviceat Grosvenor chapel, known as the American church, before attention turned to St Paul's cathedral.

At the heart of the service was a sermon by Canon Mark Oakley, the cathedral's treasurer, who was in New York at the time of the attacks. Speaking of the importance of remembering the dead, who included a former chorister at St Paul's, he said: "We do so not out of sentimentality or show but because human remembrance has reserves, life-giving reserves, which are urgently needed if we are to do more than just survive as individuals and as a society."