Probe to focus on construction work at Royal Marsden Hospital in London where blaze ripped through roof and operating theatres

London Fire Brigade began an investigation this morning into the fire that broke out in London’s Royal Marsden hospital.

Unconfirmed reports cited construction works on the fourth floor of the hospital in Chelsea as the cause of the fire but the fire service said it was too early to tell.

Tom Chidgey, group manager of London Fire Brigade, said: “That’s speculation at this stage, fire investigation teams are on site and will be there for the next couple of days. All we are able to say at this stage is they don’t believe it to be of a suspicious nature.”

A spokesperson for the hospital said work was currently being done on some of the theatres and a diagnostic unit.

Fifty per cent of the roof has been damaged by the fire, and lower floors have sustained miner damage from falling debris.

Police have cordoned off all streets around the hospital and officers have been drafted in from Brent and Kilburn.

One nurse said there was a community spirit among staff: “Staff have been helping out even if they're not meant to be in, lending out cardigans and so on, everyone’s been really good.”

A staff scientist from Cancer Research UK laboratories near the hospital said she was evacuated. “I had my lunch yesterday, went back to work, and then we were asked to go home at 2.30 because we could smell the acrid smoke. I saw it on the news like everyone else did”.

The fire started at 1.30pm yesterday. More than 100 fire fighters tackled the blaze, which spread onto the roof.

David Brown, assistant commissioner of the London Fire Brigade, said: "A plant room has been involved in the fire but it is too early to say exactly where the fire started."

Crews were on the site overnight and the blaze is now over.

A spokesperson for the LFB said that the structure of the building caused fire fighters particular problems: “It is an old hospital in parts but its also got new wings as well, which makes our firefighting a little bit more difficult because we have to be aware of different types of hazards in different parts of the building.”

About 800 staff and 79 in-patients were removed in an emergency evacuation, with the sickest patients being transferred to nearby hospitals.

Four people have been treated as a result of the fire.

The Royal Marsden has a worldwide reputation for cancer treatment and research.