David Cameron has admitted that a future Conservative government could not promise to maintain the current level of per pupil funding to English state schools.

The prime minister said that while the overall amount spent on schools would rise, his government would freeze the current level of per pupil funding, which would result in a real-terms cut at the rate of inflation each year.

In a speech at the Kingsmead academy school in Enfield, London, Cameron said:

“The cash sum that follows your child into the school will not be cut. Because the number of children going to school is going up, this has an implication that means that in cash terms the schools budget is going to be rising.

“Now, I accept that that is a difficult decision for some schools because the amount of cash per child is not going up by inflation, the amount of cash is staying the same. But I think that schools have demonstrated, brilliantly over the last five year that they can be more efficient, they can be more effective, they can make their budgets work.”

The admission came as part of a speech where the prime minister promised to wage an “all-out war on mediocrity” in the state education system.

In a video posted to Twitter, Cameron said that schools judged to be inadequate will be forced to convert into academies and develop new plans to better serve their pupils or face a takeover by outside experts that could turn the school around.