Grenfell Tower: 149 high-rise buildings in 45 local authorities fail fire safety tests

Cladding samples tested as part of a "major national investigation" into the use of panelling on housing blocks have so far produced a 100 per cent failure rate, a Government spokesperson said.

But concerns were being raised over the efficiency of the testing process after it emerged the checks did not extend to the insulation fitted behind the cladding. Lord Porter, chairman of the Local Government Association, attacked the Government for testing only the core of the panels on high-rise blocks and not the insulation behind them, which may not be fire-resistant.

It comes after Prime Minister Theresa May told local authorities to "work on the assumption" that cladding samples would fail safety tests. Combustible cladding was thought to have aided the "unprecedented" spread of the fire in Grenfell Tower which killed at least 80 people on 14 June. But the National Housing Federation has called on the Government to stop the testing and instead focus on making people safe.

Chief executive David Orr said: "These tests were the right thing to do, but the results are now conclusive: aluminium composite material (ACM) cladding simply does not pass these tests and is deemed unsafe.

A further 450 social housing blocks are set to be checked but fears were growing that the true figure of unsafe blocks could be far higher, with private residential high rises also affected.