Mr Osborne used his first editorial in the newspaper on Tuesday to criticise the Prime Minister’s general election campaign, suggesting that it amounted to “no more than a slogan".
And he continued his assault on Mrs May on Wednesday, using his second editorial and a front page story quoting a dozen Tory MP candidates to warn the Prime Minister that she must “back down” over her plans to shake up school funding.
The Government wants to introduce a national funding formula for schools so that the money it hands out is distributed more evenly across England.
But the plans would see many schools, particularly those in urban areas, lose out with funding taken away and redistributed elsewhere.
Many Tory MPs are unhappy that the changes have not gone far enough, claiming rural schools that have long been under-funded are still losing out.
The Evening Standard’s editorial on Wednesday warns that the Government is facing its “first serious uprising of the election campaign” with a “growing number” of Conservative MPs wanting to see a “commitment to rethink the proposals in the Tory manifesto”.
It says that most people in the education sector agree that the current funding model is “outdated and anachronistic”.
But it adds: “The problem with the specific proposals put forward by the Government is that they reduce the basic funding ‘per pupil’, when a fairer formula would see that basic ‘per pupil’ element increase as a percentage of the overall grant.
“It’s time to go back to the blackboard. The Government would be sensible to listen to its own candidates and back down now. We hope it will.”
More than a dozen former Tory MPs who are standing at the General Election spoke to the Evening Standard for a front page story to call on Mrs May to rethink her plans and outline an alternative way forward in the party’s manifesto which is due to be published in the coming weeks.
Graham Brady, who until the dissolution of parliament on Wednesday was the chairman of the 1922 Committee of Tory MPs, told the newspaper: “Historically, school funding across the country has been unequal.
“It is quite right that the Government is seeking to address this with a more consistent approach to school funding according to need. But it has been obvious since very soon after the draft formula was published that it could not work in that form.
“These were proposals for consultation — I look forward to seeing revised proposals in the near future.”
Geoffrey Clifton-Brown, former MP for the Cotswolds, added: “The absolute minimum in the manifesto should be that no school loses out in cash terms.”