The hazards of ill-maintained extraction systems were laid bare yesterday after London Fire Brigade was called to tackle three separate restaurant fires in the space of just a few hours.

While investigations into the blazes are ongoing, the fire service said that at least two were due to the build-up of grease from cooking materials in the ductwork and ventilation systems.

A fire at a restaurant on Lisle Street, close to Leicester Square, took four fire engines and 21 firefighters over an hour to bring under control.

Station Manager Charlie Pugsley, who was at the scene, said that dirty kitchen extract ductwork was to blame.

“The fire involved the restaurant’s ventilation system,” he said. “Businesses should make sure their ventilation system is kept clean as a build-up of fat and grease within extract filters can lead to a fire.”

Later that afternoon, the London Fire Brigade reported that a takeaway restaurant in Southwark had been “badly damaged” following a fire caused by an accumulation of grease in the ventilation system.

The area from the ducting up to the roof of the shop was destroyed in the blaze, which was tackled by more than 20 firefighters.

The basement of a restaurant in St. Johns Wood was also damaged by fire yesterday afternoon.

The fire service confirmed that the extraction system from the basement to the first floor had been “extensively damaged”, although at this stage it is still not clear if the incident was sparked by poorly maintained kitchen extraction systems.

Experts insist it is important to keep ducting clean to prevent the build-up of cooking materials.

Gary Nicholls, managing director of professional kitchen cleaning specialist Swiftclean, said the three incidents illustrate the need to remove oil, fat and grease deposits in commercial kitchen extract ductwork on a regular basis.

“This requires specialist cleaning and different skills from those needed to keep a kitchen otherwise spotless,” he said. “The ductwork isn’t seen, but if not kept scrupulously clean, harbours the potential for a fire which poses a danger to life and limb and can represent thousands of pounds worth of damage plus a critical interruption of business to a restaurant.”

Failure to keep ductwork clean can also render the building’s insurance invalid, meaning that there may not be a pay-out in the event of the fire, added Nicholls.