Theresa May has been confronted with evidence that teachers are buying “pens, pencils and paper” out of their own pockets, because of harsh school funding cuts.

Jeremy Corbyn accused the Prime Minister of also forcing head teachers to sack staff, increase class sizes and shorten the school days, as their budgets shrink.

Seizing on a new analysis warning of the biggest cuts since the Thatcher era, the Labour leader accused Ms May of breaking another manifesto promise – to deliver “a real-terms increase in the schools budget”.

And he quoted a “heartfelt letter” from a teacher named Eileen, in which she wrote: “Teachers are purchasing items such as pens, pencils, glue sticks and paper out of their own pockets

“Parents are having to make donations to purchase books. This is disgraceful”, the letter added, Mr Corbyn said.

The attack discomforted the Prime Minister, who fell back on an insistence that budgets had been “protected” and that schools were receiving “record levels of funding”.

But this claim has been demolished by the respected Institute for Fiscal Studies (IFS), which said state schools face spending cuts of 6.5 per cent per pupil.

"This would be the largest cut in school spending per pupil over a four-year period since at least the early 1980s and would return school spending per pupil to about the same real-terms level as it was in 2010-11,” it said.

Those cuts are being imposed even before the introduction of the controversial new single national funding formula (NFF), from September next year.

That new formula has sparked a backlash from Tory MPs who have found schools in their areas losing out – with the Prime Minister widely expected to retreat.

Because its introduction is being staggered, around 1,000 schools face further cuts of seven per cent per pupil into the next decade, the IFS warned.

Speaking at Prime Minister’s Questions, Mr Corbyn said: “She was clearly elected on a pledge not to cut school funding and that is exactly what is happening.”

He also quoted head teachers in West Sussex, warning of “staffing reductions, further increased class sizes, withdrawal of counselling and pastoral services, modified school hours, reductions in books, IT and equipment”.

In reply, Ms May said the Government had a “fine record over nearly seven years”, with 1.8m more pupils in good or outstanding schools.

And she claimed: “As we said we would, we have protected the schools budget. We now see more teachers in our schools. We see more teachers with first class degrees in our schools.”

The Prime Minister also launched a personal attack on Mr Corbyn and his senior allies, pointing out that he sent his child to a grammar school, while Shadow Home Secretary Diane Abbott and Shadow Attorney General Baroness Chakrabarti chose private education for their children.

“Typical Labour: take advantage and pull up the ladder behind you,” she said.

Mr Corbyn had accused Ms May of diverting cash to “her grammar school vanity project”, with £320m allocated in the Budget for new free schools, including grammars.