DOWNING STREET admitted hundreds more schools could be affected by problems with crumbly concrete as it denied PM Rishi Sunak blocked a funding request to rebuild more schools when he was chancellor.

Jonathan Slater, who was permanent secretary at the Department for Education (DfE) from May 2016 to August 2020, said today that the Treasury knew there was a “critical risk to life” if the schools programme was not funded.

He told BBC Radio 4’s Today programme that up to 400 schools a year need to be replaced, but the DfE got funding for 100 while he was the senior official, which was “frustrating.”

“The actual ask in the Spending Review of 2021 was to double the 100 to 200 — that’s what we thought was going to be practical at first instance,” he said.

“I thought we’d get it, but the actual decision that the chancellor took in 2021 was to halve the size of the programme.”

Mr Sunak claimed Mr Slater’s attack on his record was “completely and utterly wrong,” insisting: “Actually, one of the first things I did as chancellor, in my first Spending Review in 2020, was to announce a new 10-year school re-building programme for 500 schools.

“Now that equates to about 50 schools a year, that will be refurbished or rebuilt.

“If you look at what we have been doing over the previous decade, that’s completely in line with what we have always done.”

Unions meanwhile said schools are “managing the anxiety” of parents on behalf of government and they have a right to know how the concrete crisis emerged.

The Tories have faced heavy criticism after 104 schools were told to shut building containing reinforced autoclaved aerated concrete (Raac) last Thursday.

Leaders of a coalition of education and public-sector unions wrote today to Education Secretary Gillian Keegan demanding urgent answers on the Raac “emergency,” including clarity over funding and support for schools.

The letter, from the general secretaries of school leaders’ union NAHT, the Association of School and College Leaders, the National Education Union, the NASUWT teaching union, GMB and Unison, said: “It cannot be right that school leaders and their teams are charged with making decisions about the immediate risk of harm if they discover or are concerned that Raac is present on their site.

“They do not have the relevant expertise to make such assessments.

“Our members are managing the anxiety of parents and carers on behalf of government. The least they are entitled to know, with confidence, is how they ended up in this situation when the government knew of the risks long ago.”

Sir Keir Starmer said the crisis over deteriorating concrete in public sector buildings is “descending into farce” after Ms Keegan was caught swearing about coverage of the row.

In footage released by ITV News filmed as the camera repositioned for extra shots, Ms Keegan, still wearing her microphone, criticised others and claimed the government had gone “over and above” in addressing concerns relating to the material.

She said: “Does anyone ever say, you know what, you’ve done a f****** good job because everyone else has sat on their arse and done nothing?

“No signs of that, no?”

The Labour leader said ministers appeared to be attempting to “pass the buck” for school building closures caused by the concrete issue, adding: “I think this whole situation is descending into farce.

“The government has dropped the ball here, failed to prepare.

“The Prime Minister bears responsibility for some of the key decisions along the way.”

Shadow education secretary Bridget Phillipson added: “The defining image of 13 years of the Conservative-run education system will be children sat under steel girders to stop the roof falling in.”

She said Mr Sunak “bears huge culpability for his role in this debacle.”

The Welsh government said two schools on Anglesey which had been due to open for the autumn term tomorrow would be closed temporarily.

The Scottish government has said Raac is present in 35 schools, but that none poses an “immediate risk” to pupil safety.