CHRISTMAS travellers are set to endure another day of airport chaos today with continuing thick, freezing fog leading to scores of flight cancellations.

And people taking to the roads had to contend with huge jams on major routes as those starting their festive journeys competed for space with Christmas shoppers.

For the third day running, Heathrow Airport is expected to be the worst hit, with more than 300 flights cancelled as air traffic controllers limited services because of the bad weather.

The fog is expected to have little effect on train services but motorists were warned to expect delays on the roads once again.

British Airways announced it was cancelling all today's domestic services in and out of Heathrow after axing 200 flights yesterday.

BA will be able to operate long-haul services in and out of Heathrow, but some departing passengers are expected to face delays of several hours on these flights.

Heathrow's second-busiest airline, bmi (formerly British Midland Airways) has scrapped eight flights so far today on top of 40 cancellations yesterday.

The chaos is expected to continue at other airports across the country, with Gatwick, Norwich, Southampton and Coventry all among those predicting further delays.

Passengers waited overnight in freezing conditions at Heathrow, and were offered blankets and hot drinks by BA staff.

Airport operator BAA said it was providing a range of amenities for stranded passengers, including heated marquees, blankets and ponchos, sleeping mats, children's packs and food and drink.

BA laid on coaches for 3,000 people to travel from Heathrow to Manchester, Newcastle, Glasgow, Edinburgh and Aberdeen, where flights were going ahead as normal.

Geoff Want, BA's director of ground operations, said: "We would like to apologise to all customers who have been disrupted as a result of the continuous dense fog, which is unprecedented in recent times.

"We understand that Christmas is an extremely important time of year for our customers and their families and we are working around the clock to give every assistance possible.

"We are urging our customers due to travel in the next 48 hours on short-haul services to check for the latest news on their particular flight on www.ba.com"

Virgin Trains, which operates the West Coast Main Line service between London and Scotland, said it was lifting restrictions on saver tickets for today and running extra trains.

The company said it was providing an extra 4,800 seats.

Today is expected to be one of year's busiest days on the roads as thousands of workers head home for Christmas.

The rush hour is expected to start at 2pm and last until 7pm. Yesterday, busy areas included the M25 around Heathrow and at the junction with the A1/M, the M1 near Nottingham and between junctions 8 and 11 north of London, the M4 near Bristol, and the M6 near Birmingham.

The cold snap caused bookmaker William Hill to slash its odds on a white Christmas from 16-1 to 8-1 in London, 7-1 in Cardiff and 5-1 in Glasgow.

Maurice Fitzpatrick, business analyst at finance and business advice company Grant Thornton, said: "The current three-day disruption is likely to cost the UK economy at least £8m through lost productivity.

"This figure excludes any direct costs to airlines such as lost ticket revenues, which will not be insignificant, and if the fog continues we should expect to see this figure rise by approximately £2.75m a day."