Thirteen people have died and 69 seriously injured in fires that broke out in makeshift homes across the capital, London Fire Brigade (LFB) has said.
Since 2009, there have been 438 fires in sheds and outbuildings, where people were living in "unsafe" conditions.
Five people died in 2010-11 and four lives were lost in both 2012 and 2013.
LFB said it has taken action against landlords in the capital, serving about 200 enforcement notices.
There were 96 fires in 2009-10, which dropped to 85 the following year but jumped to 104 in 2011-12.
In 2012-13, 77 fires were tackled by the brigade while the figure rose to 97 last year.
In Wandsworth, south London, a woman living in a garage under some flats was taken to a hospital in April after a candle fell while she was sleeping, causing a fire.
Last year, a man died after a fire in an outbuilding in Uxbridge, west London, where he had been living for six years. The shed, located at the back of a row of shops, had no smoke alarms and the man could not escape because of a broken lock.
The brigade said people living in makeshift accommodation rely on riskier ways of cooking, heating and lighting, making these homes "potential fire traps".
The LFB has launched an "unsuitable housing" toolkit, which it said will help council workers, firefighters, charities and the police identify dangerous living conditions and help people living in them.
Third Officer with LFB, Dave Brown, said: "It's a tragedy that in this day and age we've got people living in factories, sheds and outbuildings in scenes reminiscent of a Charles Dickens novel."
Vital safety features like fire doors and alarms "can be the difference between life and death", he added.