Flat doors in Grenfell Tower could only hold back a blaze for half the time they were supposed to, investigators have found.

Experts acting on behalf of the Metropolitan Police tested an undamaged front door from the west London block and found that it could withstand a blaze for 15 minutes - not the 30 for which it was designed.

Seventy-one people died when a fire ravaged the residential building on June 14 last year.

A vast police investigation is continuing into the causes of the fire, Scotland Yard said, as it announced the new findings.

A Met Police spokesperson said: "The Metropolitan Police Service is conducting a comprehensive investigation into what happened at Grenfell Tower in June last year.

"We have previously described that our forensic examination at the scene would be followed by a phase of offsite testing to be conducted by experts in our behalf.

"As part of this investigation, experts tested a flat front door taken from Grenfell Tower.

"The door tested was designed to resist fire for 30 minutes but during the test, it was only found to resist the fire for approximately 15 minutes, a much shorter period than expected.

"The forensic examination and testing phase is ongoing and we are not able to comment on the potential impact or otherwise that any test result may have on the overall criminal investigation.

"We have shared this information with the Ministry of Housing, Communities and Local Government as the appropriate Government department, so that they are able to take any action required.

A Ministry of Housing spokesperson said: "Later this morning Ministers will update Parliament on an issue brought to Government's attention by the Met Police as part of their investigation into the Grenfell Tower fire."

Speaking after the investigation, Grenfell fire survivor Natasha Elcock said: "It's shocking - first the cladding and insulation then the doors, who knows what else is putting peoples lives at risk.

"It's time people lives are taken more seriously - and that includes everyone from every walk of life.

"People's homes must be made absolutely safe for them and their children.

"The Government should have improved regulations after previous fires.

"We can't listen to anymore excuses.

"Grenfell United will not stop campaigning until the lessons of Grenfell are learnt.

"Nothing can bring our loved ones back but we must make sure a fire like this never happens again."