The Labour, Conservative and Liberal Democrat candidates in London's mayoral race yesterday sought to link Mr Ken Livingstone's previous support for "direct action" with Monday's riots in the capital.
Mr Livingstone condemned the rioters as "mindless thugs" and later praised the police for their handling of the situation. But Labour's Mr Frank Dobson said Mr Livingstone's comments rang hollow and Monday's events proved him unfit to be mayor of London.
Some 95 arrests were made during the day-long "anti-capitalist" protest which degenerated into violence and left nine police officers injured, one seriously.
The Prime Minister, Mr Tony Blair, said he was appalled by the disturbances, during which the Cenotaph and Sir Winston Churchill's statue were vandalised.
After joining the Home Secretary, Mr Jack Straw, to inspect the damage, Mr Dobson declared: "The last 24 hours confirm what I have been saying all along. Ken Livingstone is unfit to be mayor of London."
He continued: "Rioters who believe in direct action smashed up property, put working people in fear of their lives, assaulted the police and defiled the Cenotaph. The police had the difficult and dangerous task of containing this outrageous behaviour.
"They are entitled to be sure that if they have to do this in future they will have the full support of the mayor of London. They have it from me. If Ken Livingstone were mayor, the police and Londoners would not be sure whose side he would be on."
As his candidate, Mr Steve Norris, vowed to ban any future May Day demonstrations, the Conservative leader, Mr William Hague, said the riots showed why Londoners should not back Mr Livingstone.
"After those riots . . . are we going to have a mayor of London, when the bricks are being thrown, whose heart of hearts is with the rioters, not the police?" demanded Mr Hague.
The Liberal Democrat candidate, Ms Susan Kramer, joined the attack, saying Monday's events were "yet another wakeup call to London".
She told a press conference: "Ken has made it clear he supports direct action and [on Monday] he got direct action. If you want to protest in this city you can, but violence is not acceptable. If you have the kind of leadership Ken offers, in a way you have given a nod to this, to say this is a city where anarchy can get a warm reception."
Mr Livingstone congratulated a police action concentrated on isolating "the small minority of determined wreckers and thugs intent on violence" from peaceful demonstrators. The Met operation, he said, "set the tone that London both upholds the right to peacefully demonstrate and will clamp down with the full force of the law on those who threaten mayhem in the capital".
But Mr Dobson insisted: "If you look at Livingstone's record on this issue there can be no doubt where he stands. When faced in the past with a choice between backing anarchists and rioters or the police, he has always sided with anarchists and rioters. His comments after the riot ring hollow when he has spent time encouraging direct action of the kind we saw on Monday."