A controversial safety report, coupled with lobbying by the timber industry, has led to the spread of a construction method not widely seen in the UK since the Great Fire of London.
BBC London has discovered potentially dangerous timber framed buildings are proliferating – but nobody knows how many there are.
The Great Fire of London in 1666 heralded in a new era of building regulations in Britain that lasted until the modern age.
Mindful of how flames had destroyed a third of the largely wooden city, building with timber frames was banned in the years after Sir Christopher Wren’s 1667 Building Act.
“If a secondary fire causes considerable damage you are duty bound to report thatâ€
Until recently, that is, because in 1999 the fire safety testers, BRE, carried out a test on a six-storey timber framed building in the controlled conditions of an aircraft hangar.
Their report said the fire was effectively contained, and the findings were then promoted by the UK Timber Frame Association [UKTFA].
It said at the time: “If you want to know how multi-storey timber frame buildings cope with fire there is one piece of research you must read.”
The 1999 report was used to justify relaxing old regulations on timber frame in housing blocks.
It led to the widespread use of buildings with timber frames for large council housing projects.
But what neither organisation mentioned was that, in the early hours of the morning after the test, the fire re-ignited.
Firefighters rushed back to the hangar, by which time the top four floors were completely burned out.
Brickwork cracked and the heat was so severe the fire officer evacuated his men for fear the building was about to collapse.
The second fire was finally reported in 2003 – by which time timber framed buildings, which are cheaper to make, were already sprouting over London for the first time since 1666.
Sam Webb is an architect who has warned about the danger of timber framed buildings.
Asked whether the 1999 report was misleading, he said: “I would have thought so knowing what I know now.
“If you have a fire test in which a secondary fire causes considerable damage you are duty bound to report that.
“You had to be a real detective to work out that the second  report was talking about the same fire as the first one.”
A London Assembly investigation into timber framed buildings was launched in 2009 after several major fires in London.
Last year two nearly-completed timber framed tower blocks in south London burned to the ground.
The first fire, in Peckham, was so severe it destroyed inhabited neighbouring buildings.
Meanwhile in 2007 a timber framed tower block in Croydon, south London, burned to the ground in identical circumstances to those in BRE’s hangar test.
The fire brigade had put out a small fire and departed. Families who moved back in had a narrow escape when it re-ignited and dozens were left homeless.
Describing the dangers, Mr Webb said: “When timber framed buildings catch fire the actual structure burns.
“That’s the last thing you want in a multi-storey building and it often leads to total collapse.”
But BBC London has learned that local authorities have no idea how many timber framed buildings are under construction or already built in the city.
After a Freedom of Information request only three London councils out of 32 – Bromley, Redbridge and Barking and Dagenham – confirmed they keep a record of numbers.
‘Quicker and cheaper’
In light of the BBC’s findings, Brian Coleman, chairman of the London Fire Authority, said: “I have always been a stern critic of high rise timber framed buildings having seen in my own area the results of a blaze.
“Sadly, these days developers looking to build things quicker and cheaper have resorted to timber.
“Supporters of timber frame buildings say once they’re built they’re completely safe. But we know people drill holes in walls which damages the building fabric and allows the timber to become exposed.”
Asked if he knew how many timber framed blocks there were in London, Mr Coleman said: “I’ve no idea, that’s the problem.
“I personally wouldn’t allow any high rise timber buildings – there needs to be a review of regulations.
“What we do about buildings already constructed I’m not sure.”
Geoff Arnold, chairman of the UKTFA, which promoted the 1999 fire test, said: “The BRE test was an assessment of the six-storey building in terms of its ability to withstand the 60 minute compartment fire test – in this regard it was successful.”
Of the second fire, he said: “It was not referred to in the report as it had little relevance to the outcome of the impact of fire in the very specific test.
“Timber frame is used around the world and is generally accepted as the future of construction.”
A BRE spokeswoman said: “BRE has issued all information it was able to issue resulting from these projects.
“Other information that came out was given to project sponsors.
“BRE cannot publish this information independently.”