Thousands of people may be living in potentially dangerous tower blocks after at least 11 buildings were revealed to have combustible cladding similar to that thought to have fuelled the Grenfell Tower fire.
The high-rise blocks are in eight local authority areas in England and include Camden, Manchester and Plymouth, Communities and Local Government Secretary Sajid Javid said in a letter to MPs.
Landlords, typically local authorities and housing associations, have been asked to check if they used similar aluminium composite material (ACM) panels to Grenfell Tower, where 79 people have been confirmed dead or listed as missing presumed dead after a devastating fire last week.
Landlords are being urged to send samples as a "matter of urgency" to the Government's testing facility, which can handle around 100 samples per day.
But just because a building fails the Government test to determine whether it has combustible cladding does not mean it is unsafe, with that to be determined after more checks by the fire and rescue services, Theresa May's deputy spokesman said earlier.
Mr Javid said the Grenfell Tower disaster had "shaken my comprehension of what it means to be in office".
"This Government will do everything possible not just to replace houses and provide immediate relief, but to seek justice for those people who have been failed.
"This tragedy should weigh on the consciousness of every person tasked with making a decision so this can never happen again."
The 11 buildings confirmed by the Government to have combustible cladding include the Chalcots Estate in north London, which is removing the cladding, and three 16-storey blocks in the Mount Wise Tower Estate in Plymouth.
Another high-rise block is in the Manchester area.
Separately, Newlon Housing Trust confirmed the 22-storey tower block Rivers Apartments, in Tottenham, north London, was clad with Reynobond PE - the same cladding reportedly used on Grenfell Tower.
But it said, after an "extensive safety audit", London Fire Brigade confirmed the tower block would be considered a "low fire risk" after modifications and technical clarifications.
The housing association was awaiting recommendations from experts to determine whether the cladding should be replaced, the trust added.
Some 600 high-rises are believed to have cladding, but the Department for Communities and Local Government (DCLG) would not reveal how many samples have been tested in total, saying the priority was to give updates on failed tests and for councils to inform their residents.
Local authorities are discussing potential contingency plans with landlords and the DCLG in case large numbers of residents have to move out of their blocks if fire brigades deem them unsafe, Downing Street said.
In other developments:
:: It emerged that as well as being combustible, the insulation in the Grenfell cladding released highly toxic gas and some victims were treated with the hydrogen cyanide antidote Cyanokit.
:: The renovation work carried out on Grenfell Tower before the fire was inspected 16 times by the council.
:: NHS England said that 10 patients were still receiving care across four London hospitals. Five of these are in critical care.
:: Almost £1 million has been distributed to affected families, with 354 households within the cordon area placed into emergency accommodation.
:: The Government announced victims have had outstanding energy bills written off by power companies.
:: Birmingham City Council leader John Clancy said all 213 blocks in the authority's area would be fitted with sprinkler systems regardless of whether the Government would pay.
Mrs May promised that "no stone will be left unturned" in the inquiry, as she updated MPs in the House of Commons on Thursday.
Labour leader Jeremy Corbyn told MPs: "At least 79 people are dead. It is both a tragedy and an outrage because every single one of those deaths could and should have been avoided."
Nicholas Paget-Brown, the Conservative leader of Kensington and Chelsea council has faced calls to resign after chief executive Nicholas Holgate was forced to quit by Mr Javid following intense criticism of its handling of the crisis.
Mr Paget-Brown has apologised for a "failing in our collective response" to the fire, admitting co-ordination on the ground could have been better and re-homing people was not "as fast as we would have liked".