Combustible cladding on apartment towers in England is more widespread than first thought.

Flammable cladding's being seen as a big factor in London's deadly Grenfell apartment fire.

UK correspondent Ben Bland told Rachel Smalley 600 towers are being tested, seven have already been found to have that cladding.

"I saw images in one council area with that cladding already being removed because of the concerns about it. That local authority, which is in London, said that it wasn't the cladding they had specified when they signed off the development."

LISTEN ABOVE AS BEN BLAND SPEAKS TO RACHEL SMALLEY

Last week's Grenfell Tower inferno was Britain's worst blaze since World War II.

Theresa May says local authorities are doing everything to make towers safe.

But CNN's Phil Black said there's a lot more to find out.

"It's an estimate. The cladding is similar, not exactly the same, so now they have to begin the process of determining how combustible, or whether that same risk does in fact exist and in how many of these properties."