The academic achievements of these schools are still unclear, but Mr Blair and his advisers have defended their performance. In his “legacy” speech to the Specialist Schools and Academies Trust conference in Birmingham yesterday, the Prime Minister said he wanted 400 academies to serve struggling areas - an increase on the previous target of 200 - by 2010.

It would mean one in 10 secondaries would be an academy, with a nationwide increase in the involvement of business and faith-group sponsors of state education. Firms such as Unilever, Microsoft and Exeter university would fund new the new trust schools, which have similar freedoms to the academies on curriculum and staffing.

According to the Government’s special adviser Sir Cyril Taylor, the schools justify high investment through their improving GCSE results. Thirty-nine per cent of pupils at academies achieved five good GCSEs this year, compared with 27 per cent for the last year before they changed over, provisional figures show.

Speaking to the 2,000-strong conference, Mr Blair said his nine years of “education, education, education” had required the Government to start by addressing systemic failure and introducingcentral direction and targets.

Labour then addressed years of under-investment with substantial spending on teachers, classrooms and ICT.

He said the monolithic comprehensive system had been reformed by offering a spectrum of options, such as specialist schools and academies, to address pupils’ personal needs. Academies, he said, were giving hope and belief to parents and pupils in deprived areas.

Speaking before the Prime Minister’s address, Sir Cyril said there were almost 400 poorly performing schools, many of which were not making significant headway towards improving their results.

About half were earmarked to become academies but the other half would benefit from joining trusts with stronger schools, he said - a move that is now easier under the new Education Act.

Sir Cyril drew particular attention to the Ninestiles Federation, in Birmingham. Since taking on responsibility for Waverley school, it has seen the number of pupils getting five good GCSEs increase from 16 per cent to 75 per cent. Results at the International school, which joined the federation in September 2003, have risen from 9 per cent to 51 per cent this year.

He encouraged headteachers to consider proposals for schools to share more responsibility with social services for children in care, especially in providing pastoral support. He also called for some young people in care to be placed in boarding schools.

Sir Cyril praised the specialist schools’ initiative, which he said had succeeded “year in and year out” in terms of raising standards. But he said it was important that schools should continue to justify the additional investment by sharing their expertise and facilities with their communities.