The Government admitted on Saturday night that it has failed to order compulsory testing of combustible insulation material used in tower blocks in a move branded "ludicrous" by safety experts.

It came as cladding samples from 34 high-rise buildings in 17 local authorities were found to have failed safety tests in the wake of the Grenfell Tower disaster which killed at least 79 people.

Experts said that perhaps of even greater concern is the failure to order the testing of the insulating material which lies behind the panels and is potentially even more flammable.

The danger of insulating material was confirmed by early tests on the panels used to clad Grenfell Tower ordered by the Metropolitan Police, as part of their criminal investigation into the disaster.

Detective Chief Superintendent Fiona McCormack, who is leading the investigation, said preliminary tests on the insulation showed it combusted soon after the fire started.

She said initial tests of the cladding also failed the safety test. She added that the insulation proved “more flammable than the cladding”.

The implications of the failure to test the insulation is that tower blocks may pass safety tests based on cladding while still retaining potentially combustible material.