Union leaders from across the UK have written a letter calling on the new Conservative government to “fully protect” all areas of education funding over the course of the Parliament.

After gaining a surprise majority in the House of Commons on Friday, the Tories are likely to implement a raft of cuts to the public sector.

Ahead of the general election, prime minister David Cameron said he would protect per-pupil funding in schools, but admitted it would not rise in line with inflation. There were no such commitments to early years or post-16 education, however.

Schools fear their budgets will be even more tightly squeezed over the next five years, owing to decisions made by the previous coalition government. The move to increase national insurance and pension contributions is likely to lead to a 5 per cent cut to their coffers.

An independent study by the Institute for Fiscal Studies showed that the spending pledges of all three main parties could lead to cuts to school budgets of up to 12 per cent.

In a joint letter from 10 unions from all four corners of the UK - including the ATL, the NUT and the NAHT - teachers’ and heads’ leaders have warned that without urgent action from the new government, students will see “bigger class sizes, fewer teachers and lecturers and a reduced curriculum”.

The letter states: “The first test of the Conservative Party’s intentions towards education will be whether it will act to fund additional costs and protect all education funding, regardless of sector, age or location.

“Spending on education is an essential investment in the future. Our first focus must be on the value of education, rather than its cost.”

And it adds: “Ensuring that schools and colleges have the resources to educate our people should be a priority for every political party, just as it is for our organisations. We urge the new government to ensure that education funding is prioritised and fully protected.”