LONDON (Reuters) - Cladding on 120 different tower blocks has failed fire tests in the wake of a blaze that killed 79 people in London, showing a widespread breach of British building regulations over previous decades, Prime Minister Theresa May said on Wednesday.

At least 79 people died or are missing and presumed dead following the Grenfell Tower fire, which rapidly spread through the 24-storey block as families and children slept. Police have said that the death count could rise further.

May said that the cladding - panels put up on the outside of buildings to improve their aesthetics and energy efficiency - was not compliant with regulations. The manufacturer has since halted sales of the panels.

May said the test failures showed that there was a wider fire safety issue that was the result of failures over many decades.

“As we have seen from the number of buildings where the cladding has failed the combustibility test ... this is a much wider issue,” May said.

“It’s an issue that has been continuing for many years, for decades, in terms of cladding being put up in buildings. There are real questions, as to how this has happened, why it’s happened and how we can ensure that it doesn’t happen in the future.”

May clashed with opposition Labour leader Jeremy Corbyn, who criticized cuts to local government and fire service budgets.

“This disaster must be a wake-up call,” he said.

May has pledged to rehouse all residents who have lost their homes within three weeks - a target which Corbyn said she was at risk of missing.

“At the moment, it doesn’t look anything like that target is going to be achieved,” Corbyn said.