Gloves are off as Ken accuses Boris of 7/7 smear on Islam

The Tory candidate said he took "deep offence" at Ken Livingstone's claim he had said the Koran was "inherently" violent.

However, the Mayor insisted Mr Johnson's remarks - in contrast to his own rousing response to the 7 July attacks - showed his true reaction to the tragedy.

In the first radio hustings on LBC radio between the three main candidates, Mr Johnson insisted he would have issued "exactly the same" kind of remarks after the bombings, which killed 52 people, as Mr Livingstone had if he had been running the city at the time.

"What Londoners want in the event of a tragedy of that kind... is someone who will speak for the city and give a voice to our defiance and our unwillingness to submit to that kind of terror and kind of cowardly attack," he said.

However, the Mayor claimed: "I know what Boris would have said because he wrote it in the Spectator the following week. Very different. I said this is a criminal act by a handful of men. It doesn't define a faith or an ideology.

"What you said, Boris, was Islam was the problem... And the Koran is inherently violent. I actually made certain that we were looking at individuals. You smeared an entire faith."

An audibly furious Mr Johnson responded: "Can I tell you what deep offence I take at that? I think you really traduce what I said.

"My view is that Islam is a religion of peace and indeed I am very proud to say I have Muslim ancestors.

"My great-grandfather knew the Koran off by heart, Ken Livingstone, and I really wish you would leave off these kinds of tactics, which demean this race and demean your office."

In an article for The Spectator magazine the week after the bombings, Mr Johnson wrote: "The Islamicists last week horribly and irrefutably asserted the supreme importance of that faith, overriding all worldly considerations... Islam is the problem.

"To any non-Muslim reader of the Koran, Islamophobia - fear of Islam - seems a natural reaction... "

However, he added: "Last week's bombs were placed neither by martyrs nor by soldiers, but by criminals. It was not war, but terrorism, and to say otherwise is a mistake and a surrender."

Lib-Dem candidate Brian Paddick, who was the Met police spokesman after the attacks, said he would have said: " These people cannot bow Londoners."

The rivals also clashed over Mr Livingstone's tearful apology for slavery, which he made on the 200th anniversary of the abolition of the trade last August.

Backing him, Mr Paddick said: "OK, it's nothing to do with us at the moment but there is a serious concern by some people about what has happened in the past. It is right to apologise for what's happened."

However, Mr Johnson said he would not have apologised, adding: "I wouldn't have gone down that route because I think what you're doing is getting into a culture that entrenches and feeds grievances rather than trying to reconcile people."

Mr Livingstone came under pressure from LBC presenter Nick Ferrari to discuss his five children by three different women but insisted: "I have a very good, happy, extended family and we're happy with that arrangement. I'm not going to talk about my private life."

All three candidates said they would still attend the Olympic opening ceremony in Beijing this summer despite Gordon Brown's decision not to do so.

The radio debate came after Mr Johnson was booed and heckled last night at the biggest hustings of the race so far.

The visibly nervous Tory, faced with a hostile audience of 2,500 Londoners, admitted: "This is the most wonderful and intimidating event I've ever been at."

Mr Livingstone also attracted controversy by agreeing to give failed asylum seekers free travel to attend immigration interviews.