A "major national investigation" must take place into the decades-long use of potentially flammable cladding on high-rise towers across the country, Prime Minister Theresa May has said.
Mrs May's call came as Cabinet was informed 95 samples of cladding from tower blocks in 32 English local authority areas have failed fire safety tests - amounting to 100% of all samples submitted by councils.
The PM's official spokesman said the national investigation could be conducted as a second phase of the public inquiry already announced into the Grenfell Tower blaze, which claimed the lives of at least 79 people.
The latest tally of fire safety checks was presented to Cabinet by Communities and Local Government Secretary Sajid Javid, who has issued an urgent call for all councils to send in samples of cladding from tall buildings.
Schools and hospitals may also do the same where they have concerns, with the Care Quality Commission having contacted more than 17,000 care homes, hospices and private hospitals to tell them to check fire safety procedures.
The figures emerged as a fire safety expert raised doubts over the combustibility tests being carried out on cladding samples by the Building Research Establishment (BRE).
David Metcalfe, head of the Centre for Window and Cladding Technology, a body which works with hundreds of contractors, architects and manufacturers, claimed samples are being tested "severely" in a way which may be inflating the scale of the crisis.
Regulations in force refer to insulation products and filler materials, but do not specifically state that cladding should be of limited combustibility, he said.
The Department for Communities and Local Government responded by saying an independent panel of experts had approved the test, while the BRE did not comment.
The PM's spokesman told reporters evidence suggests the use of the suspect cladding stretches back at least into the last decade.
Characterising the Cabinet response to the mounting evidence of widespread problems, he said: "It is clear that everybody is concerned about this and everybody wants to establish what went wrong."
Three towers in Newham, east London, and two in Sefton, Merseyside, are the latest to be identified as at-risk, the DCLG said.
It came as housing group One Manchester said 16 of the high-rise buildings it owns have now been found to be encased with combustible material.
Meanwhile, new figures released by the Home Office on Tuesday showed the number of fires in high-rise purpose-built flats fell by almost half in the years leading up to the Grenfell Tower disaster.
Fears have been expressed that contractors might have been confused by cladding with a category zero rating - meaning it has high fire resistance but is still flammable - mistakenly thinking this meant it was non-combustible.
The exact nature of the Government-backed tests has not been made public, but Mr Javid confirmed samples are being ranked on a scale of one to three - with those in categories two and three considered a failure.
Mr Metcalfe told the Press Association: "All these products are failing, which I don't think is any great surprise. The bigger issue is that it is not entirely clear whether or not the products, in accordance with the regulations, have to be of limited combustibility in the first place.
"Timber isn't an insulation product, it's not a filler material, so there's nothing stopping you using timber on a high-rise building, but the Government now are saying that all cladding should be of limited combustibility - there is a massive inconsistency there."
The Government is applying a "strict" interpretation of rules contained in an "unclear" regulatory document, Mr Metcalfe went on.
"They are interpreting that document to say the cladding should have been of limited combustibility but it doesn't actually say that," he said.
"They are testing it more severely than might have been done in the past because people didn't think it required that level of testing."
His analysis follows claims on Monday by Housing Minister Alok Sharma that building regulations were "very clear" the type of cladding used at Grenfell Tower was "non-compliant" on buildings more than 18 metres (59ft).
Many councils have responded to news that their buildings' cladding failed fire tests by saying the non-combustible material used in the insulation mitigates the risk of flames spreading.
Asked if this means the tests are making the risk to public safety appear greater than it is, Mr Metcalfe said: "What they are doing is probably about right, but it doesn't necessarily reflect what is going to happen on a building.
"You are testing a material in isolation. What we need to consider is how it performs as a system - it's the cladding, it's the support system, it's the insulation, it's the cavity barriers, it's all of these things combined that determines what happens in a fire."
Meanwhile, a residents' group has written an open letter to Mrs May and Home Secretary Amber Rudd, demanding immediate funding for legal advice for bereaved families and survivors.
It said: "The investigation must leave no stone unturned. 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 number of displaced households now in emergency accommodation following the fire has risen to 386, the Grenfell Response Team said.
It added in a statement that more than £1,680,000 has been handed out to those affected by the blaze.
On Tuesday afternoon, work started to remove the cladding from the Hanover tower block in Broomhall, Sheffield, after it failed the new tests.
Mrs May said "something has clearly gone wrong" with the use of potentially flammable cladding on high-rise towers across the country.
"What we have seen from the investigations that have taken place of cladding material in tower blocks across the country is that 100% of these materials being combustible," the Prime Minister said during a visit to a secondary school in Bristol.
"Something clearly has gone wrong over a number of years and we need to find out what, why and how to make sure it doesn't happen again."