Shadow chancellor George Osborne also pledges to do away with the planning gain supplement if the Tories win the next election.

Shadow chancellor George Osborne has pledged to rethink the definition of green-belt land in a bid to build more affordable homes and to do away with the planning gain supplement if the Tories win the next election.

In a speech this week, he said the PGS was a return of the development land tax. He added: "That's something that all Labour governments try when they run out of money."

He also said that the Tories would look with "fresh eyes" at the definition of greenbelt land on the edge of towns and brownfield sites.

"Too often our current system protects the marginal scrubland because it is greenfield while at the same time lets precious urban spaces like gardens get built over because they are labelled brownfield.''

He said that Tory policies on housebuilding would allow many more young families who are currently priced out of the market to aspire to the "dream of home ownership", with the expansion of shared equity schemes.

Osborne pledged to concentrate Tory housebuilding policy on suburban homes, but would not be drawn on precise details of the plans.

He said: "We should be looking at the decaying suburbs with the same energy that we have redeveloped city centres."

Osborne also attacked chancellor Gordon Brown's handling of real estate investment trusts, but said: "We want REITs to work and to be a success."