Insulation fitted to Grenfell Tower gave off a highly toxic cyanide gas which may have led to the deaths of some of the 79 confirmed victims, it's been claimed.

An expert has claimed insulation boards fitted to the outside of the building during a previous makeover produce a deadly gas when they burn.

Potentially every flat could have been filled with enough gas to kill those inside, The Sun newspaper reports.

The horrific revelation comes as the chief executive of Kensington and Chelsea council resigned amid criticism over the borough's response to the deadly blaze.

Nicholas Holgate stood down from the position, saying that staying would be a "distraction" to the recovery process.

In a statement, Holgate said the council's "highest priority" was to help families affected by the fire.

The Sun reports that at least three of those injured in the fire have been treated with an antidote for hydrogen cyanide poisoning in hospital.

However, it's feared the number of those affected could be higher.

The gas could have incapacitated some residents, but linking it to the cause of death may be impossible because of the condition of the victims.

London's King's College Hospital confirmed to Sky News UK that three of the 12 patients it received from the fire were treated with the hydrogen cyanide antidote Cyanokit.

An initial 68 patients were taken to six hospitals across London, with 18 receiving critical care.

The insulation fitted to Grenfell Tower was made of Polyisocyanurate (PIR) - a rigid plastic foam sandwiched between two sheets of aluminium foil.

 

Grenfell Tower in west London after a fire engulfed the 24-storey building. (Photo \ AP)

The boards were fitted behind the cladding that was installed to improve the appearance of the building.

Richard Hull, professor of chemistry and fire science at the University of Central Lancashire, told Sky the gas produced by the insulation when it burned may have been deadly.

"The outside wall of the building had 150mm of PIR foam (fitted), and once the fire had spread to that every flat would have its own source of PIR foam, which would have produced enough hydrogen cyanide to kill all the people in that flat," he said.

Professor Hull co-authored a leading study in 2011 into the fire toxicity of six insulation materials which was published in the journal Energy & Building.

The study established that PIR was the most toxic.

Professor Hull said: "It's been an accident waiting to happen and unfortunately we've got to the stage now where the accident has happened and we're standing here saying 'I told you so'.

"It would have been much better if people had listened to us earlier on when we published the report."

Efforts to assist survivors continue, with some now-homeless former Grenfell residents offered housing in a luxury complex nearby.

The Sun reports some of the residents forced to leave their homes will be permanently housed in Kensington High Street in a £2 billion ($3.4 billion) development.

Hundreds of people were left with nowhere to live after the blaze destroyed their West London tower block, leaving 79 people missing and presumed dead.