Planning, preparation and assessment became an election issue this week as Tony Blair said: “We need to make sure it is properly done.”

He was responding to comments from Chris Luck, headteacher of Eastfield primary, Enfield, north London, who said his salary budget needed to be increased by 10 per cent in order to provide cover.

The Prime Minister told a press conference at Lilian Baylis school in south London: “This is something I will talk about with Education Secretary Ruth Kelly. It is extremely important that teachers get this preparation time as it is something they value. It is a question of how we allocate the money in the education system.”

His words will be seized upon this weekend in Telford, Shropshire, as the National Association of Head Teachers meets for its annual conference.

Last month the union defied its leadership and voted to pull out of the workforce agreement over funding. And Mick Brookes, who will take over as general secretary in September, caused a major upset when he trounced David Hawker, director of Brighton and Hove children’s services, running on a pull-out ticket.

He is expected to tell conference that thousands of schools will be unable to provide half-a-day’s PPA time for every teacher this September, and is backing a call contained in two of the motions for enough money to allow schools to use qualified teachers for PPA cover. That would significantly harden the NAHT’s position and bring it almost in line with the National Union of Teachers, which never signed the deal and opposes anyone but qualified teachers taking whole classes.

But figures released this week, showing English primary schools have almost pound;750 million squirrelled away, with average surpluses of almost Pounds 50,000 each, will be embarrassing to heads who claim they do not have the money to implement the scheme.

In Wales, figures published earlier this year showed primary schools sitting on reserves averaging pound;24,600 each and totalling pound;41.2m.

David Hart, in his last conference as general secretary (see below) is expected to say that the association shot itself in the foot by withdrawing from the workload agreement. He said this week that some schools could close on Friday afternoons to deliver PPA and warned ministers that there could be an “autumn of discontent”.

But delegates looking for practical advice on how to deliver PPA from the National Remodelling Team will be disappointed. The agency, responsible for helping schools to implement the deal, has boycotted the conference, following the association’s withdrawal.

Meanwhile, Margaret Evitts, head of Gungrog Church in Wales nursery and infant school, in Welshpool, will propose a motion supporting the development of the new play-based foundation stage for three to seven-year-olds.

But she will question whether sufficient funding will be available for the extra outdoor and classroom space and the one-adult-to-eight-pupils staffing ratios needed in schools, when the pilot scheme is rolled out nationally.