The Government will block the sale of school playing fields unless the money is used to improve sports facilities.

Even then, local authorities will have to show they have exhausted all other funding possibilities and demonstrate that the school will be left with adequate outdoor facilities, under the guidelines which will be introduced next month.

Mr Clarke hopes the move, supported by the National Playing Fields Association (NPFA), will silence critics who claim the Government has so far to meet its manifesto pledge to halt the sale of school playing fields.

Elsa Davies, outgoing director of the NPFA, said: “On the last day in post, it warms my heart enormously to know that in future school playing fields will only be lost in the most extreme circumstances.”

School sport is moving up the political agenda as the Government attempts to show it is serious about tackling child obesity. It is considering including a promise to make all schools offer competitive sport in its election manifesto.

Reports suggested that Mr Clarke is resisting the plans because he fears they would place additional burdens on teachers and the curriculum.

A Department for Education and Skills spokesman said: “We do not do third-term speculation. The Government is committed to competitive sport.

More than 90 per cent of schools currently engage in competitive sport.”

Andy Burnham, MP for Leigh, one of the backbenchers pushing for a manifesto pledge, told the Fabian Review that schools should run representative sports teams from the age of seven. Teachers should be paid to take after-school sports clubs.

But Chris Keates, National Association of Schoolmasters Union of Women Teachers’ acting general secretary, said: “The key to increasing the participation of primary school pupils in sport is not to place additional burdens and expectations on teachers, but to look more creatively at how specialist coaches and sport and leisure centres can support teachers and schools in providing more curriculum balance and enrichment.”