Bill Greenshields, president of the National Union of Teachers (NUT) and a former English teacher at Ilkeston School, said the plan was a backdoor attempt to privatise state education.

At the NUT's annual conference in Manchester, he said: "A simple message to the individually and corporately rich, who are backing the school privatisation programme: our communities do not want their schools sold off.

"If you really want to support education as you claim - try paying your taxes."

Academies were first introduced nationally in 2002, in a drive to replace failing comprehensives in the poorest areas of England.

Sponsors, usually affluent business figures or church groups, can gain control of the running of an academy in exchange for an investment of up to £2 million.

Private schools and universities, however, do not have to pay to become academy sponsors.

The government funds the building costs of new academies, typically £25 million, and the running costs.

During the conference, Mr Greenshields said private schools should be abolished and brought under state control.

He also called on ministers to focus on ending child poverty and tackling the widening social class divisions in society.

He said: "The target of halving child poverty by 2010 must not be relegated to another Government aspiration.

"Action to achieve it would have a real impact on children's chances in education."

Members of the NUT are still casting their votes nationally to decide whether or not to strike on April 24 over this year's projected 2.54 per cent pay rise.

The union is demanding a 10 per cent pay rise, or £3,000 for every teacher this September, whichever is greater.

It has announced it will prepare for a ballot of its 255,000 members on a series of possible strikes in England and Wales after a planned one-day strike.