Cheap but flammable

The same type of cladding believed to have contributed to the Grenfell fire is on at least 52 tower blocks in London, a BBC investigation has found. "We learned in the Great Fire of London it's not a good idea to clad buildings in flammable material."

Grenfell Tower was encased in panels made up of aluminium sheets with a polyethylene core, which melts and burns at extreme temperatures. Fire safety expert Arnold Tarling, a chartered surveyor, said: "It's like cladding your home in solid petrol."When it becomes liquid it melts, burns and sets fire to polyethylene at higher levels.The BBC has now found it on buildings owned by councils, housing associations, and companies. Some may not be removed. Heated to half the temperature of a typical house fire during a test by Itri Laboratories, they melted and burst into flame.

Polyethylene-based cladding was found on 24 council tower blocks, 23 housing association buildings, and five privately-owned high rises. However, the true figure is likely to be considerably higher, as numerous local authorities and housing associations refused to give the BBC an answer.

Figures suggest its use in construction is rising:

• 2008: 140 metric tonnes.
• 2013: 170 metric tonnes.
• 2018: 190 metric tonnes (projection based on polyethylene sales already made).

The BBC has also discovered that dozens of planning applications for recladding have been submitted in the capital since the fire. Most were not for tower blocks, but smaller homes, offices and shops.

Mr Tarling said: "There will certainly be other properties out there that haven't been identified. And I don't see why it becomes safe at lower levels - the speed of fire spread is so fast it will move on before the fire brigade arrive."

Nationwide, cladding samples from 294 buildings have now failed government flammability tests - but it was not revealed how many were polyethylene-based or made of other materials. In London, more than half of the 88 buildings that were tested failed.

Polyethylene has become widespread because it is cheap and durable. Although it can be treated to make it less flammable, the added cost means this is often not done. Despite concerns over polyethylene cladding, the BBC was able to easily obtain numerous panels from suppliers that arrived without guidance or warning.