Both Labour and the Liberal Democrats have underestimated the cost of expanding free school meals - in policies that could leave schools burdened with extra costs and having to cut back on provision in other areas, it is claimed.

According to a report by the politically neutral Education Policy Institute (EPI), published today, both parties have calculated the cost of free school meals expansion using 2012 prices, and have failed to factor in the rising costs, particularly of labour, resulting from the introduction of the minimum wage.

While Labour has pledged to put in £850 million for free school meals, the EPI report said that figure is £140 million short. And while the Lib Dems have pledged £1.15 billion, the EPI said that is £180 million short. 

Lib Dem manifesto: Skills wallets and funding

Labour manifesto: A National Education Service and adult education

Conservative manifesto: £3bn for ‘national skills fund’

Jon Andrews, deputy head of research at the EPI, said schools would either have to meet the cost from elsewhere in the budget or cut back on what they’re offering.

He said: “Free school meals expansion comes as a considerable cost pressure which is built into both of their [Labour and Lib Dem] assumptions but we think they are potentially underestimating the true cost of meals. The cost of a free school meal has been set at £2.30 since 2012 - it’s not been uprated to reflect increases in costs or in particular labour costs.”

Other manifesto “flaws” that could affect disadvantaged pupils, as outlined by the EPI, include:

• The Conservative Party’s plan for extra funding is “skewed away from disadvantaged pupils”.

• The party has no plans to address weaknesses in the system such as off-rolling, which “in particular impacts vulnerable pupils”.

• The Conservatives’ early years policy focuses on “childcare” rather than “early education”.

• Wording of the Conservative manifesto ”leaves the door open to expand or create new grammar schools which would widen the disadvantage gap”.

• Under Conservative and Lib Dem plans, pupil premium would see a real-terms fall of nearly 15 per cent between 2015 and 2023.

• Labour and Lib Dem plans to reform the accountability system could affect the attainment of disadvantaged pupils - for example: “Plans to end primary assessments risk having a limited measure of pupil progress between primary and secondary, and teacher-moderated assessments risk introducing teacher bias against certain groups of pupils”.

• None of the three main parties has a clear and coherent strategy for addressing the uneven access to good schools, nor do they commit to reviewing the current admission code.

• None of the parties addresses the challenge of getting the best teachers into the best schools.

A Lib Dem spokesperson said: “As well as extending free school meals to every primary school child and almost 900,000 more of the poorest secondary school children, we have budgeted to keep the cost per meal rising with prices every year.”

He said the Lib Dems would keep the value of the pupil premium “under review”, adding that they would triple it for preschool children and extend it to colleges for the first time.

On accountability, he said: “We know that a child’s time at school can’t be measured just by a week of tests.”

Labour and the Conservatives have been contacted for comment.

The Institute for Fiscal Studies yesterday said the costings of the Labour and Lib Dem free school meals plans were plausible.