Conor Ryan: All parties are making promises they cannot keep

When the Tory leader of Kent County Council, Paul Carter, warned that the Conservatives' free schools policy threatened funding for local authorities and other schools, he had a rare success highlighting a hidden truth behind the parties' education policies: they are making promises in today's election that they can't really keep.

Free schools are affected by a black hole in Tory school funding. The Liberal Democrats can't guarantee lower class sizes, and Labour has published pupils' and parents' guarantees with no real means of enforcement. Michael Gove tried to bat off suggestions on Radio 4 last week that there was no money to fund his flagship policy. But while the Conservatives have said that they would raid Labour's school building fund to pay for capital costs for parent-led schools, they have not said how they would cover extra day-to-day costs.

Instead, as Mr Carter rightly recognised, they have promised to top-slice local authority budgets to fund pupils at the new schools. However, there would be costs in maintaining surplus school places to increase choice and in continuing to fund local authority schools functions, such as admissions, school buses, truancy wardens and special needs. Gove is likely to need £1bn a year for revenue costs extra if his policy is to succeed.

All three parties propose some form of pupil premium which would give schools extra money for pupils from poorer backgrounds. At present, many schools get more money in deprived areas, but good schools in more affluent areas get little extra to attract poorer pupils. The pupil premium would overcome this. However, as it will effectively provide new subsidies to schools in the suburbs and shires, the Liberal Democrats have said it will cost £2.5bn a year, and they have suggested ways they might fund it.

The Tories have given no details of how they would fund their premium. With the free schools shortfall this means there is likely to be a £3.5bn black hole that Gove says will come from cuts in areas not part of the schools budgets. While some may come from axing quangos like the curriculum authority, it could also mean cuts in youth services, education maintenance allowances for sixth formers, the teachers' pension fund and teacher training budgets if there is to be no new money for the education department.

But the other two parties have their own credibility gaps too. Nick Clegg, the Liberal Democrat leader, insists that his party will cut class sizes and introduce one-to-one tuition for struggling pupils. He has described it as one of his top priorities. What he really means is that his £2.5bn pupil premium, once it is distributed to schools, could be used for these purposes. Or it might not: it may instead be used to prevent cuts in basic staff budgets at a time of increasing austerity.As the Liberal Democrats have an aversion to central prescription, they have no idea what the money will actually be used for. The Scottish Nationalist Party promised to cut infant class sizes to 18 in 2007. As good localists, they gave the money to local authorities with few strings. The result was that councils spent the money elsewhere, teacher numbers fell and there was no improvement in infant class sizes. The minister responsible was demoted.

Labour has suffered from the opposite problem. It has adopted a more centralised approach to schools of which the pupil and parent guarantees are its flagship manifesto commitment. Intended to support parent power, the guarantees on everything from pupil detention rules to one-to-one teaching were included in Labour's last schools bill but ran out of time in the Lords once the election was called. But the schools department had already issued an 80-page blueprint, the detail of which had spread alarm among head teachers who have grown used to growing autonomy. In reality, the guarantees are more likely to frustrate parents as there is little indication of how any of their new commitments can be enforced: they are unlikely to stand up in court.

The parties' problematic promises owe a lot to two factors that will affect the direction of education policy, whoever wins today. The first is that budgets will inevitably be much tighter as public spending is cut to rebalance the books. And the second is that all three parties support school structures – including academies – where heads and governors call the shots rather than ministers or councils. These are the realities that will really decide schools policy over the next four or five years.

The writer is a former senior education adviser to Tony Blair and David Blunkett, and blogs at http://conorfryan.blogspot.com