Interview by Mihir Bose BBC sports editor

Prime Minister Gordon Brown has built in this huge contingency for just about everything that could go wrong London Mayor Ken Livingstone

London Mayor Ken Livingstone says it would be a "defeat" if the Olympics in 2012 end up costing more than �7bn.

A revised �9.35bn budget was officially announced in March by Olympics minister Tessa Jowell but Livingstone told BBC Sport: "It is completely excessive.

"I'll consider it a personal defeat if we do not knock several billion off."

Demolition work begins on the main site of the Olympic stadium on Thursday - Friday marks five years to the day before the start of the London Games.

Interview: Mayor of London Ken Livingstone

The Olympics had been estimated at costing �2.4bn when London initially won the right to host the event two years ago.

606: DEBATE Give your thoughts on the 2012 budget

The revised �9.3bn figure was first revealed by the BBC earlier this year and then confirmed later by Jowell.

That figure included a �2.7bn contingency amount and also had new costs for such items as regeneration and infrastructure built into it.

But Livingstone insisted: "We've now got a budget set for �5.5bn. Inevitably, things will crop up and it will almost end up at �6bn. I'd be quite proud if we kept it at that.

"If it starts going over �7bn that will be a defeat.

"Prime Minister Gordon Brown has built in this huge contingency for just about everything that could go wrong.

"Our job is to keep that to the minimum of things that could go wrong."

Livingstone admitted he did have reservations about the scale of the project to start with, but that the progress made since had eased his concerns.

"I was much more worried two years ago when I thought, having won it, that there was so much we had to do.

Livingstone says he "exploded" when he saw the 2012 Olympics logo

"But here we are and we have achieved every one of our targets and milestones.

"I remember coming back from Singapore thinking, would we get the stadium finished on time?"

"Now it will be in operation almost two years before the Olympics when we finish building it so I can't believe how well things have actually been going."

Referring to the 2012 logo, which has come in for heavy criticism, Livingstone says he has "come to tolerate it" despite having initial reservations.

"I'm the mayor of a city and the only thing any mayor wants in the logo is the name of the city enormous and predominant," he said.

"I didn't get that so I was a bit grumpy about that.

"It was hidden from me up until about the last two weeks and it was too late to do anything about it.

"I exploded pretty much as dramatically as the rest of the country when they saw it.