Squash house prices at your peril, Boris Johnson tells the coalition

He warned the Government that proposals to deliberately "flatten" the market could lead to a sharp spike in prices as the economy improved.

The Mayor said that the move would be "risky" in the short term as it would damage the confidence needed for economic recovery. And he predicted that asking the middle classes to "wean" themselves off house-price inflation was "unachievable" in the longer term.

Mr Johnson urged ministers to focus their attention on building affordable homes - for rent as well as purchase - instead.

Writing in his Daily Telegraph column, he said: "If you tell people it is government policy that their house should effectively fall in value, then you will punch that confidence in the solar plexus - and you will make them less likely to invest, to take on new ventures and new staff.

"If the housing market tanks, then the financial system tanks too. People will be unable to get the mortgages to buy new homes, and developers will be unable to get the finance to build them, and the problem of supply will get even worse."

He added: "The best way to help those millions in search of an affordable home is not to try vainly to ensure that the present stock of housing becomes more affordable - ie falls in value - but to increase the supply of affordable homes."

Mr Johnson's warning comes after it emerged that he was living in a rented flat just down the road from his £2.3million north London marital home. Sources close to the Mayor denied he was kicked out by wife Marina Wheeler, a barrister, after claims that he had an affair last year.

One said: "The idea is to have a little space to work things through. I'm confident this is not a permanent arrangement."

Mr Johnson, 46, understood to have a short-term tenancy on the flat, has been there for a couple of months. He was pictured leaving the property with his bike over the weekend.

However, the Mayor is a regular visitor at the family home and the couple have been seen playing tennis together in recent weeks. In August, weeks after reports of the affair emerged, he went on a Tanzania holiday with his wife and four children.

Mr Johnson's official spokesman said: "We never comment on the Mayor's private life."