Britain’s education minister Gillian Keegan apologised for an expletive-ridden outburst on Monday after complaining she wasn’t being thanked enough for doing a “fucking good job” in dealing with potentially hundreds of unsafe school buildings.

The revelations of old and weak concrete in schools, which saw 104 ordered to shut buildings only days before the start of a new term and others using rooms propped up by steel girders, has sparked anger among parents and teachers.

The issue is a new political headache for Prime Minister Rishi Sunak as members of parliament returned on Monday following the summer recess and adds to the impression of decaying public infrastructure in Britain.

The government is awaiting responses from about 1,500 schools that were sent surveys to identify those with Reinforced Autoclaved Aerated Concrete (RAAC), a lightweight form of concrete commonly used during the 1960s-80s but now considered weak and unsafe.

Keegan risked inflaming the debate further in unguarded remarks caught on camera following an interview with ITV when she suggested she had done more than others to try to resolve the issue.

“Does anyone ever say ‘you know what, you’ve done a fucking good job, because everyone else has sat on their arse and done nothing?’,” Keegan, Britain’s fifth education secretary in two years, said. “No signs of that, no?”.

Keegan later apologised for using “choice language” and said her comments were “unnecessary”.

Sunak’s spokesperson said the language was “not acceptable” but that the prime minister was satisfied with her apology.

Opposition parties said the school closures were evidence of under-investment in public services by the Conservative Party, which has been in power since 2010. Labour leader Keir Starmer said the government’s handling of the school closures was “descending into farce”.

Sunak told reporters that 95 per cent of the roughly 22,000 schools in England would not be affected, and issues could be limited to single classrooms in many cases.

His spokesperson said the number of schools affected would be “in the hundreds not the thousands”.

The former top civil servant in the education department said that Sunak, in a previous job as finance minister, had halved annual funding to repair schools when officials had asked for it to be doubled.

“I was absolutely amazed to see … the decision,” former Permanent Secretary Jonathan Slater told BBC Radio.

Asked if he was to blame, Sunak said it was “completely and utterly wrong” and that the funding he approved was in line with decisions taken over the previous decade.