"There is poor visibility so the number of flights that are landing and taking off at the airport have been reduced as a precaution," a spokesman for Heathrow said. "The problem is expected to ease later this morning".

The problem is exacerbated because Ferrovial's Heathrow is operating at close to full capacity, the spokesman added. Britain's coalition government blocked the airport's expansion in 2010.

Some flights at London's City Airport and Manchester airport in north west England have also been cancelled.