A rise in the number of cannabis farms in London is to blame for a spate of house fires across the capital, according to figures.

According to the London Fire Brigade, there was a fire at a house used to produce cannabis on average once a fortnight in 2012, more than double the number from 2010.

Police say they have also closed down more than 440 cannabis factories across London since September 2012, including one raid of a farm in Bromley on 21 November.

Fire officers said the lighting and heating equipment to grow the plants are the main reasons for the blazes at the farms.

Police and the London Fire Brigade are now asking members of the public to be on the lookout for any signs there might be a potentially dangerous cannabis factory in their area.

The Fire Service said to be aware of key signs, such as a sickly-sweet smell, constant intense lighting at the property, covered windows or windows with high levels of condensation.

London Fire Brigade Third Officer Dave Brown said: "They're often in top floors or lofts which means when a fire takes hold it spreads, destroying roofs and damaging neighbouring buildings."

Detective Chief Superintendent Carl Bussey, who leads Operation Hawk to tackle drug-related crime, added: "Cannabis cultivation and drug dealing damage communities and generate organised and violent crime, money laundering and anti-social behaviour."

The problem of cannabis farms catching fire is also occurring across the country. This month, firefighters were called to an address in Smethwick in Birmingham following reports of a fire.

Police initially thought a firework was responsible for the fire, but officers then discovered a cannabis factory inside and believed that to be the true cause.

A family of five in Burnley, Lancashire described how they were left homeless after a fire broke out at the cannabis factory in a house next door, which eventually ripped through to their own home in October.

Members of the public who have information about anyone who is dealing drugs in their area are urged to contact their local Safer Neighbourhoods Team or dial 101, the police non-emergency number.