Non-contact time for teachers became an election issue this week, as Tony Blair said: “We need to make sure that 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 a 10th to enable him to provide cover for planning, preparation and assessment time.

The Prime Minister told a press conference at Lilian Baylis school in south London: “This is something I will talk to Ruth Kelly about. 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 we have got in the education system.”

His words will be seized upon this weekend in Telford, Shropshire, as the National Association of Head Teachers meet for their 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.

He is expected to tell the conference that thousands of schools will be unable to provide half a day’s PPA time per teacher this September and is backing a call, 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.

Brendan Hassett, head of Dolphinholme primary, Lancaster, who is proposing one of the motions, said: “If we go down this road (of using support staff for PPA cover) my concern is that in the future the Government will say you have done it for 10 per cent, now do it for 20 per cent and save some money.”

David Hart, in his last conference as general secretary, is expected to say that the association shot itself in the foot by withdrawing. 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. Mr Hart described the decision as “childish and petty”.

In his speech, Mr Hart will challenge the Government’s push for parent power, saying they are often part of the problem. In March the association had to deal with 20 cases of assault by parents or pupils. One included death threats. Heads reported that they and their families have been harassed at home with the police having to be called in.

He is due to say: “Giving more power to those parents who lack responsibility is like putting an alcoholic in charge of a bar.”

He will call for slimmed-down governing bodies and for the appointment of staff to be left to heads and their leadership teams.

John White, NAHT president, is expected to accuse Charles Clarke, the previous education secretary, and Ruth Kelly, of being “sadly lacking”. He will dub Ms Kelly “Calamity Jane” and attack her for failing to implement the Tomlinson report on 14-19 education.

Tim Benson, head of Nelson primary, East Ham, London, will draw attention to research he helped to compile showing that 60 per cent of schools’

chairs of governors feel the overall quality of candidates for headteacher posts is poor and many have to advertise three or more times. There will also be calls for the Government to abandon plans to increase the teacher pension age to 65 and for more funding for the inclusion of violent and disruptive pupils.