A fire that killed at least 79 people at a London tower block started in a fridge freezer, and the outside cladding engulfed by the blaze has since been shown to fail all safety tests, London police said on Friday.

Investigators said they would consider bringing manslaughter charges over the disaster and had already seized material from a number of undisclosed organisations.

Detective Superintendent Fiona McCormack said experts had now concluded the fire, the mostly deadly blaze in London since World War Two, had started in a Hotpoint fridge freezer, model FF175BP, which had not been subject to any recall.

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.”

Britain ordered an immediate technical examination of the Hotpoint fridge model to establish whether further action should be taken, but said there was no need for owners to switch off their appliances.

“We are working with the authorities to obtain access to the appliance so that we can assist with the ongoing investigations,” said Whirlpool Corp, the world’s largest maker of home appliances which owns the Hotpoint brand in the Europe and Asia Pacific regions.

In the United States, the brand now belongs to Haier, following the Chinese group’s purchase of General Electric Co’s appliance business.