Theresa May has called for a "major national investigation" into the use of potentially flammable cladding in high-rise towers in the wake of the Grenfell fire.
The PM's move came as samples of cladding from 95 buildings all failed safety tests introduced since the fire - a 100% failure rate.
The 95 buildings were across 32 local areas.
A Number 10 spokesperson said: "The Prime Minister said there would need to be a major national investigation into what had gone wrong when cladding which is failing the tests had been fitted on buildings across the country over a number of decades."
External cladding was blamed for the rapid spread of the fire at west London's Grenfell Tower on 14 June.
At least 79 people are feared to have died in the disaster, though officials have warned that the number could go up.
The Government has rejected any suggestions of a cover-up in the number of people killed in the fire.
"Nobody is hiding anything," Defence Secretary Sir Michael Fallon told Sky News.
"But it is very hard, sadly, for the recovery operation when they are dealing with bodies that have been completely destroyed by fire, that may not be complete," he added.
"Secondly, nobody knows exactly how many people were sleeping in that tower that particular night."
Earlier Labour MP David Lammy suggested the real number of people killed in blaze could have been covered up because of fears of riots.
"What people say is that if you put the numbers out early, there could be civil unrest. That's what they say," he told BBC2's Newsnight.
"I am sympathetic to it, I am going to walk alongside those people."
Mr Lammy, MP for Tottenham and who lost a friend in the fire, said there was a "gap" between what witnesses and residents had said and what the official figures showed.
"In one flat alone, people say there were up to 40 people gathering, because they gathered in the flat, it was Ramadan," he said.
"When you have tragedies of this kind that could have been prevented, we know from Hillsborough and other affairs in our national life that governments, local authorities, big corporations, companies, the contractors - they cover their backs. That's why I raised issues around the documentation."
In the aftermath of the disaster, he called on the Prime Minister and Metropolitan Police to seize all relevant documents.
A group of the tower block residents has written to Mrs May and Home Secretary Amber Rudd asking them to make sure "justice is served for everyone on the estate" following the fire.
"The investigation must leave no stone unturned," said the letter, written on behalf of the residents of Hurstway, Testerton, Barandon and Grenfell Walks on the Lancaster West estate.
"It must identify each and every individual and organisation who must bear responsibility and accountability for this tragedy and the mishandling of the aftermath."
The residents' group, which is part of the Justice4Grenfell campaign, also lamented what it called "the paucity of support" families received by the state in the immediate aftermath of the tragedy.
Prince Charles visited a relief centre helping survivors from the tower fire, and praised volunteers for their "fantastic" work.
The Prince of Wales met with some of the survivors of the deadly fire and looked at the thousands of tributes laid in memory of the victims at the site.
As president of the British Red Cross, he has made a donation of an undisclosed amount to the relief effort - one of the three major funds for people affected by the fire.