Investigators say they will consider bringing manslaughter charges over the London tower block fire that killed at least 79 people.
The outside cladding engulfed by the blaze has since been shown to fail all safety tests, police said on Friday. They have already seized material from a number of undisclosed organisations.
Detective Superintendent Fiona McCormack also said experts had now concluded the fire, the mostly deadly blaze in London since World War II, had started in a fridge freezer.
The blaze has provoked anger and heaped pressure on Prime Minister Theresa May, who is fighting for her political survival after her party lost its parliamentary majority in a snap election at a time when Britain is beginning divorce talks with the European Union.
The speed at which the fire engulfed the 24-storey Grenfell Tower raised questions about the external cladding on the block.
Asked if the insulation and aluminium tiles used were acceptable for such buildings, McCormack told reporters: "No they're not."
"All I can say at the moment is they don't pass any of the safety tests. So that will form part of what is a manslaughter investigation."
As well as possible manslaughter, police will consider health and safety offences and breaches of other building regulations.
McCormack said all companies involved in the building and refurbishment of the building would be reviewed.
Britain also ordered an immediate technical examination of the Whirlpool company's Hotpoint fridge model FF175BP, which had not been subject to any recall to establish whether further action should be taken, but said there was no need for owners to switch off their appliances.
Whirlpool Corp's share price had dropped by 4 percent on Friday, wiping almost US$500 million (AU$660 million) off the company's value.
"We are working with the authorities to obtain access to the appliance so that we can assist with the ongoing investigations," said Whirlpool, the world's largest maker of home appliances.
"Words cannot express our sorrow at this terrible tragedy," Whirpool said in a statement.
The fire has acted as a focal point for anger at local authority funding cuts and, if more buildings are deemed unsafe, the government faces the task of rehousing people within existing social housing facilities which are stretched.
The government said it was urgently conducting tests on some 600 high-rise buildings in England which have exterior cladding, often added to insulate them or improve the external appearance of ageing blocks. Some councils have begun removing the panels.
Problems have so far been identified in 14 buildings in London, Manchester and elsewhere in England, it added.
Grenfell Tower, in north Kensington, west London, had undergone an £8.7 million pound refurbishment which was completed in 2016, but residents of the more than 120 apartments had complained about its fire safety.