Campaigners fighting the construction of a 24-storey tower block in Swiss Cottage were handed what could be a major victory yesterday after the Mayor of London said a decision on the scheme “was a matter for Camden Council”.

Boris Johnson appeared to distance his office from any decision made on the erection of the tower at 100 Avenue Road, allaying fears he was preparing to override the council should it decide to reject the planning application.

Campaigners welcomed the Mayor’s comments as a “defeat for Essential Living” - the developers behind the proposals - but said the “war was not yet won”.

Mr Johnson’s remarks came following a question by Conservative London Assembly Member Andrew Boff on the development.

The Mayor said: “The crucial point to make is that this is a decision for Camden and it is a borough that is not within my control or indeed the conservative party.

“It is up to them [the council] to decide what they want to do.

“I would urge local people who feel strongly about this matter to make representations to them.”

Labour councillors have previously been encouraging residents to write to the Mayor’s office to oppose the scheme, saying this was “where the real power lies”.

But Mr Johnson said the notion that the GLA would definitely be deciding on the scheme was “complete nonsense and a flat out lie”.

He added: “There is a democratic system, everybody knows how the planning process works.

“Camden Council has a responsibility and they must discharge that responsibility.

“If they choose to throw out the scheme it is entirely a matter for them.”

Sarah Gottlieb, of the Save Swiss Cottage campaign group, heralded the comments from the Mayor, adding: “This is proof protest can work.

“We were particularly heartened to hear Boris urging residents in Camden to make representations to the council on the scheme.

“We echo this.

“We’ve won a battle but now we need to go on and win the war.”

But the Mayor did not – and, according to fellow Conservatives, could not – go as far as to say he would not use powers to overrule the council’s decision should they reject the application.

Andrew Dismore, Labour London Assembly Member for Barnet and Camden, asked a number of times for the Mayor to commit to not overruling any decision made by Camden Council.

Mr Dismore said: “I regret to say the Conservative Assembly member raised the planning application in a very party political manner, trying to pin the entire responsibility for the decision on Camden Council.

“When I questioned the Mayor myself, he accepted that he had issued the stage 1 determination, which approved the scheme in principle.

“Whilst he repeatedly asserted the planning application was for Camden to decide, he refused to answer my question, which I put to him five times, as to whether he would undertake not to call in the decision, if Camden were to refuse it.

“It was clear to me from the exchanges therefore, that if Camden were to refuse it, the Mayor would almost certainly overrule their decision - just as he has called in the decision over the Mount Pleasant planning application.

“The only option for those who have concerns about the scheme seems to me to be for Camden to impose the strictest planning conditions it can, and to hope the Mayor does not overrule these.”

But Mr Boff said he was “almost certain” he would not call-in the council’s decision.

“I’d put money on the Mayor leaving the decision up to Camden Council,” he said.

“In his six years of office he has never called in a scheme as small as the Avenue Road development.

“For others to suggest he would call it in is quite ridiculous.

“Let’s be clear - the ball is in Camden Council’s court.

“If it approves the planning application, the tower will get built. If it rejects the application, it won’t.”

The date for the planning application to go before the council was set for July 31.

This has been pushed back to an as-yet unknown date.