Keir Starmer has piled pressure on Rishi Sunak over the concrete crisis in schools, accusing the Tories of acting like “cowboy builders”.
More than 100 schools were last week ordered to either completely or partially close over safety fears.
Classrooms across England were found to have been built using reinforced autoclaved aerated concrete (RAAC), with a full list being published on Wednesday morning.
The Health and Safety Executive has warned the material can “collapse with little or no notice”.
Speaking during the first PMQs since the summer break, Starmer tore into the prime minister for his handling of the danger.
“The truth is this crisis is the inevitable result of 13 years of cutting corners, botched jobs, sticking plaster politics,” the Labour leader said.
“It’s the sort of thing you expect from cowboy builders. Saying everyone else is wrong and everyone else is to blame.
“Pretending they have done an ’effing good job even if the ceiling falls in.”
Starmer added: “The difference is in this case The cowboys are running the country.
“Isn’t he ashamed that after 13 years of Tory government, children are cowering under steel supports stopping their classroom roof falling in?”
Sunak said he had “swiftly acted” to fix the problem in some schools as the expert advice on RAAC “changed over time”.
And the prime minister criticised Starmer for not having raised the issue in the past.
“This is exactly the kind of opportunism we expect from Captain Hindsight,” he said.
The government has been under intense pressure all week, with education secretary Gillian Keegan having been caught on camera saying she deserved more credit for doing a “fucking good job”.
Sunak has also been personally implicated in the row after he was accused of having rejected calls from officials for 200 schools a year to be replaced when he was chancellor. Instead, he only gave the green light for 50.
This morning, defence secretary Grant Shapps also acknowledged the problem is likely to extend across all of the public sector, with “virtually all estates” having buildings that used RAAC.