Fog paralyses London's Heathrow airport again

"The weather across much of the UK is regrettably showing little sign of improvement," said Geoff Want, director of ground operations for British Airways, which has cancelled all domestic flights.

Boeing 747 Jumbo jets are being put on some European routes to try and deal with the backlog.

On Thursday, 350 flights were cancelled and a similar number will be stopped on Friday, said a spokesman for airport operator BAA, which runs Heathrow and six other airports in Britain.

"It is the world's busiest international airport but we have only two runways. If you compare with our main competitors in Europe, Frankfurt has three, Paris has four and Amsterdam has five. We have fundamental capacity constraints," BAA spokesman Simon Baugh told BBC radio on Friday.

British Airways had to despatch more than 3,000 passengers on coaches across Britain as the airport was gripped by fog for a third day running.