Boris pledges 'first-time homes for Bridget Jones'

In his first major policy speech as a candidate, Mr Johnson said more homes are needed because the size of the average household is shrinking.

Speaking to the National House-Building Council (NHBC), he said: "Over a quarter of London's first time buyers are now single women, up from only 15 per cent in the 1980s. Bridget Jones wants a place of her own."

He added that longer life expectancy means that "we are not just talking about granny flats; we are talking about great granny flats. London's housing crisis is one of the biggest deterrents to talent and one of the biggest causes of unhappiness."

But the solution lay in working with London boroughs, "not bullying them, and not getting hung up on percentages of affordable accommodation", he added.

He highlighted Hammersmith and Fulham, recently vilified by the Mayor. "They have actually built so many more houses than expected that they will more than break their target for new affordable homes even if the percentage is less than 50 per cent," he said.

He noted that Wandsworth's "Hidden Homes" policy, creating new homes to rent in existing council estates, "has led to the construction of more council properties than any other council in London" - but has also been snubbed.

"I will be willing to ease those quotas - but only in order to encourage development. Because, in the words of one councillor, 50 per cent of bugger-all is still bugger-all," he said.

He also promised to protect London's traditional and historic buildings and streets from bulldozers and skyscrapers.

Mr Johnson said he would assure Londoners that "their gardens, their views, their neighbourhoods are not going to be dwarfed by high rise blocks or engulfed in a sea of identikit homes.

"What the average Londoner wants is a house with a garden and a front door. But when I look at some of the plans for the 27 phallocratic towers that Ken wants to erect in the suburbs, I wonder whether we have learned anything from the experience of the last 50 years.

"So why is the last Victorian terrace in the Isle of Dogs being torn down to be replaced by a high-rise?

"We seem to be in the grip of barbarians who are determined to knock down venerable buildings - Victorian police stations and swimming baths - and put drab blocks in their place.

"You can have more houses without wrecking the garden city of London."

Meanwhile the Mayor, on tour in India, published new figures showing that 4,686 new homes for shared ownership were completed in 2006/7, the highest ever figure.

Mr Livingstone defended his 50 per cent "affordable" target.

"My tougher targets are helping to make many more lower income Londoners homeowners." he said.

"Giving up the 50 per cent target would mean fewer homes for affordable shared ownership and renting."