Downing Street has revealed that 600 high-rise buildings have similar cladding to Grenfell Tower.
No.10 made the revelation this morning, citing council estimates.
This comes after Theresa May revealed that tests on Britain's tower blocks show some of them are fitted with "combustible" cladding.
Follwing the tests, carried out in the wake of last week's Grenfell Tower tragedy, the Prime Minister said "all possible steps" are now being taken by local authorities and fire services to ensure buildings are safe. Residents have also been informed.
May has also announced that immigration checks won't be carried out on those who have been affected by the tragedy, nor will checks be conducted on those providing "vital" information to identify victims or assist in the criminal investigation.
She made the comments in a statement to the House of Commons, claiming "no stone will be left unturned" in the inquiry into Grenfell Tower fire. "For any guilty parties," she said, "there will be nowhere to hide."
The Prime Minister expects an interim report to be produced as "early as possible" by the chair of the inquiry.
She also said: "All social landlords have been instructed to carry out additional fire safety checks on tower blocks and ensure the appropriate safety and response measures are in place.
"We've also taken steps to make private landlords aware and make our checking facilities available to them for free.
"The House should, of course, be careful on speculating what caused this fire. But, as a precaution, the Government has arranged to test cladding in all relevant tower blocks.
"Shortly before I came to the chamber, I was informed that a number of these tests have come back as combustible.
"The relevant local authorities and local fire services have been informed, and, as I speak, they are taking all possible steps to ensure buildings are safe and to inform affected residents."