The figures came as he continued to face questions over his role in the debacle, with a minister telling Sky News the former chancellor only approved funding for the rebuilding of 50 schools yearly when he was in charge of the Treasury, despite a bid for 200.

Politics live: Keegan faces more mockery after social media post

In further developments on Tuesday, embattled Education Secretary Gillian Keegan was mocked over a graphic that claimed "most schools are unaffected" by reinforced autoclaved aerated concrete (RAAC).

Labour was quick to post a spoof saying "most beachgoers not eaten by big shark", in reference to the stance of the mayor in the movie Jaws.

Meanwhile, a letter seen by Sky News from NHS England to trusts has told them to bolster their emergency plans if RAAC is present in hospitals, following the new government guidance to schools.

The unsafe concrete forced the full or partial closure of over 100 schools in England this week due to fears it could collapse.

The government has been accused of failing to heed repeated warnings about the material, with critics blaming the problem on a lack of investment into public infrastructure.

Sky News has learnt that a "massive" school rebuilding programme launched in 2020 to rebuild 500 schools within a decade has taken off to a slow start.

The plan was for schools to be rebuilt and refurbished at a pace of around 50 a year, but the Department for Education confirmed that just four schools have been completed since the first round of applications was launched in 2021.

Officials insist the programme is on track, and that they are still confident of "ramping up" to an average of 50 per year.

A report by the National Audit Office, which scrutinises government spending, in June warned that there were concerns about the schools programme.

They said by March of this year the department had awarded just 24 contracts against a forecast of 83, due to "instability in the construction sector and inflationary risks".

But a Downing Street spokesperson said while just four had been solely rebuilt, refurbishments were under way in many other schools.

And a spokesperson for the DfE said: "We have committed to rebuilding 500 schools under the Schools Rebuilding programme between 2020 and 2030 and are on track to deliver that commitment.

"Awarding contracts and establishing projects takes time but we have made rapid progress and are exceeding delivery timescales compared to the previous Priority School Building Programme, while delivering schools that will be net zero in operation. The Infrastructure and Project Authority has also highlighted the strength of the SRP's progress."

Sunak 'gave less funding than requested' for crumbling schools

It came as schools minister Nick Gibb admitted that his department had bid for 200 schools a year to be rebuilt, in a case made to the Treasury two years ago.

But Mr Sunak, who was chancellor at the time, approved just 50 - despite the senior civil servant in the department, Jonathan Slater, warning of a "critical risk to life".

Mr Gibb sought to defend the prime minister, telling Sky News it was "simply not true" to say he oversaw budget cuts and that 50 a year was in line with previous austerity years.

He said: "We put in a bid for 200, but what Rishi agreed to was to continue the rebuilding programme with 50 a year, consistent with what we'd been doing since we came into office.

"We put in a bid for 200, but of course, the Treasury then has to compare that with all the other priorities from right across Whitehall, from the health service, defence, and so on."

Labour's Jonathan Ashworth, who was made shadow paymaster general in Monday's reshuffle, said it was "the most startling fact of the day".

He told Sky News: "You've got the schools minister to admit that they asked for more investment to fix schools and Rishi Sunak's cut it back, so the buck stops with him. Schools have had to close and roofs are being held up with steel girders."

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Hospitals told to prepare for RAAC failure

Ministers have said that hundreds more schools may be impacted by RAAC - which was widely used in buildings from the 1950s to the mid-1990s.

There have been warnings about the material for many years, but the government said "new evidence" emerged over the summer about the dangers it poses - prompting them to order schools to close areas where it is present.

Experts have warned the problem could be far wider than schools, with RAAC present on hospital and court buildings, for example.

NHS boards have now been told to ensure checks on their estates are being carried out ahead of a previously set deadline for the end of this week, and to plan for cases of RAAC failure.

A letter seen by Sky News said that management plans should already be in place in hospitals where there is known RAAC but "In light of the need to maintain both the safety and confidence of staff, patients and visitors" - trusts should make sure those plans are "sufficiently robust and being implemented".

It goes onto say a regional evacuation plan has been created and tested in the East of England and boards should "familiarise" themselves with the exercise even if they don't have known cases of RAAC.

It adds: "This exercise is, however, essential for those organisations with known RAAC, and should be done as a matter of priority if it has not already been completed."