On your marks: the great Christmas getaway starts

Around 600,000 were expected to fly out of Heathrow airport, while almost two million motorists were hitting the roads in one of the busiest days of the year.

Hundreds of thousands of City workers were leaving the capital for one of the longest break in years, as the recession forced many companies to offer extended holidays.

The Federation of Small Businesses said that "more members than ever" were closing for at least a fortnight, between 22 December and 5 January.

But experts said that congestion at airports and on the road and rail networks will be less than in previous years, with holidaymakers having the opportunity to stagger their journeys over a longer period.

As Christmas Day falls on a Thursday many people will be travelling early next week as well as over this weekend.

Airports especially were expecting passenger numbers to be down. Heathrow, Gatwick and Stansted and the Association of British Travel Agents said that the winter season had seen a four per cent drop in the number of foreign holidays taken.

Travel agents have not been helped by capacity cuts made by tour operators and the fall in sterling that has seen the cost of holidays soar.

While 16 million people were expected to take to the roads over the Christmas period, experts said the getaway would be less frantic this year.

Gavin Hill-Smith, from the AA, said: "We expect a rush at 3pm today because that's when the schools close, but people will be leaving any time between now right up to Christmas Eve.

"We're not expecting any one day to be the busiest, as it will be more staggered right across from the Sunday to the Wednesday." The busiest days would be the 22nd, 23rd and 27th, he added.

The exodus by train is expected to be huge, with 22 million people across the country using the train network.

New figures show 50,000 more people are visiting St Pancras International station each day, compared to an average month.

The Association of Train Operating Companies said today and tomorrow would be their busiest day, with longer distance services being especially busy.

Chief executive Michael Roberts said: "The railways are gearing up for a major Christmas getaway.

"In the week leading up to the holiday, we expect as many people to travel by train as those who flew in and out of Manchester Airport in the whole of 2007."

Some cheap tickets are still available, however. Tickets for a London to Bristol service that leaves today at 12pm are now £13.50, while a single to Liverpool for the same day is £61.60.

Ben Pearson, commercial director of ticket company thetrainline.com said prices would rise sharply if passengers left it too late to book tickets.

He said: "The cheap fares are selling out. Based on the day of the week Christmas falls, we can anticipate the busiest and most expensive travel dates. We can predict there will be thousands travelling on 20 December."

Travellers are, however, facing the possibility of delays over Christmas because of extensive shutdowns on lines.

Large sections of the Tube and National Rail network are to be shut for four days for maintenance work from 25 to 28 December and some London commuter lines will be closed for up to 11 days.

Engineering work is taking place at 60 sites on the West Coast main line between London and Scotland, meaning the possibility of delays for passengers.