The campaigners have been on the pitches in Wembley, north-west London, for more than three weeks, in opposition to Brent council’s proposals for a new school. They object to private sector involvement in education and complain of a lack of consultation.

Their action was highlighted this week at the National Union of Teachers’

conference, where delegates attacked the planned expansion of the academies programme.

Hank Roberts, from Brent NUT, accused Brent council of refusing to consult properly on whether the proposed school should go ahead or not.

“This is a travesty of democracy and governance by diktat,” he said. “No wonder people have had to resort to direct action.”

The sponsor of the academy, millionaire property developer Andrew Rosenfeld, was caught up in the cash for honours row after it was revealed he had made a secret loan to the Labour party before the last general election.

Delegates accused other local authorities of trying to stifle criticism of the privately-sponsored schools and of using “heavying” tactics.

Labour-led Lancashire council has threatened to stop a teacher taking time out for union activities if he continues publicly criticising the council’s academy plans, a letter leaked to The TES shows.

John Bangs, the NUT’s head of education, said the threat to Ken Cridland was undemocratic and showed the pressure being passed on to local authorities from the Government.

On June 12, representatives of 32 local campaigns against academies are to present their cases to an informal MPs’ commission of inquiry at Westminster.

The NASUWT teachers’ union was also critical of academies at its conference in Belfast. Chris Keates, the general secretary, said that although “the wacky and downright weird sponsors had all but disappeared”, the programme still exemplified the union’s greatest fears about private sector involvement in education.

“We have philosophically and resolutely opposed the concept of academies because they compromise national pay and conditions and have implications for wider social cohesion,” she said.

Ms Keates told Alan Johnson, the Education Secretary, to protect schools from privatisation just as he had helped block the privatisation of the Royal Mail when he was a union leader.

Mr Johnson said that eight out of the 45 academies had not automatically recognised teacher unions, but said their managers would have no choice if more than half of their staff were members of a union and held a ballot.