Heavy snow has caused further disruption across Britain.
Councils say they are running out of grit to keep roads open. A shortage of salt is looming. Fresh falls of snow are expected in southern England on Friday morning.
Transport Secretary Geoff Hoon told the BBC the Highways Agency was putting 25,000 tonnes of salt on main roads a day, but producers could deliver only 30,000 tonnes a week.
He said the agency has five days reserve of salt, although that has been reduced to four days in areas where supplies have been given to councils running short.
The Local Government Association said more grit has been put on roads in the last four days than all last winter.
Many flights were delayed or cancelled at Luton, Birmingham, East Midlands and Aberdeen airports.