The frontrunners in the race to become prime minister have put promises to increase school funding at the forefront of their campaigns.

Former foreign secretary Boris Johnson today used a column in the Daily Telegraph to pledge that thousands of schools would get “much more per pupil”.

His comments followed this weekend’s promise from former education secretary Michael Gove to increase school funding by £1 billion.

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However, Jules White, the leader of the WorthLess? headteachers’ campaign for school funding, warned that “the numbers sound grand but, in reality, they may not be anywhere near enough”.

School funding has emerged as a prominent issue in a Conservative Party leadership campaign that has otherwise been dominated by Brexit.

It shows the salience of an issue that was credited with causing 750,000 people to switch their votes during the 2017 general election, helping to deprive the Conservatives of their Commons majority.

Mr Johnson, a two-term Mayor of London, today writes it is “simply not sustainable” that per-pupil funding was £6,800 in some parts of London, and £4,200 in other parts of the country.

He says the answer is “not to split the difference, but to level up”, and adds: "I pledge significantly to improve the level of per pupil funding so that thousands of schools get much more per pupil - and to protect that funding in real terms."

He does not give a figure, but the Telegraph says it was understood that he would like every secondary school in England to spend at least £5,000 per pupil.

In his column, Mr Johnson also raises the issue of teacher pay, without making an explicit promise to increase salaries.

He writes: “It should be obvious to all Conservatives that teachers are performing the most vital and indeed the most conservative function: transmitting knowledge from one generation to the next. It is accordingly obvious that they should be decently paid.”

Mr White, who last year led a march on Westminster by 2,000 heads, told Tes it was “welcome news” that “the importance of school funding is finally being recognised at the top levels of government”.

He added: “Care must be taken, however, as some of the commitments appear to lack meaningful substance. The numbers sound grand but in reality they may not be anywhere near enough.

“Since 2015, schools have been deprived of billions of pounds worth of funding, whilst major costs have added to our financial woes.

“Also, schools are being asked to routinely cover the work of other services such as social care and even the police.”

Other Tory leadership contenders have also called for increased school funding.

Esther McVey, a former work and pensions secretary, has pledged an extra £2 billion for schools and £2 billion for special educational needs and disability and further education as part of her leadership campaign.

She said this would come from freeing up £7 billion from the foreign aid budget.

Ms McVey has previously raised school funding in Parliament.

Housing minister Kit Malthouse’s campaign website says: “I will increase funding for schools significantly, prioritise support for parents, and tackle child poverty.”

Another candidate, James Cleverly, does not mention school funding on his campaign website, but he has twice written to the UK Statistics Authority to complain that statistics about school funding on the School Cuts website were “inaccurate”.