LONDON - Around 18 million people are expected to hit the roads on Friday with jams predicted during the afternoon as the Christmas getaway begins.

Millions more will also take to trains or planes, but all could be hit by roadworks, strikes and cancellations.

The early exodus has been caused by Christmas Day falling on a Tuesday with just one in four people expected to be working on Christmas Eve, according to office supplier Regus.

The Highways Agency said two thirds of major roadworks on England's motorways and major A roads would be completed or suspended over Christmas and New Year.

However, works will remain in place at 36 locations on some of the busiest roads, such as the M25, M4, M56, A1, and A3.

"The roads will be busy, so we urge drivers to plan their journeys and leave extra time to travel safely at this busy time," said Roads Minister Tom Harris.

Motoring organisation the RAC said the rise in fuel prices would deter some motorists using their cars but still warned there would be jams.

"If you are travelling by car this Christmas, try to avoid the busiest time, which we predict will be 3pm on Friday, December 21, when an estimated 18 million cars will take to the road to drive home for an extended Christmas break," said an RAC spokesman.

Meanwhile the Association of Train Operating Companies (ATOC) said up to four million people would take to the train, a million more than on a typical weekday.

"With more people taking two weeks off, we are expecting many passengers to travel on the Friday and Saturday before Christmas," said George Muir, director general of ATOC.

"We strongly advise people to book ahead and reserve seats wherever possible."

While some firms are relaxing ticketing restrictions to allow passengers to use Saver tickets at peak times, there will be problems, with engineering work taking place on some busy routes including the West Coast mainline.

The millions who are expected to fly out of Britain could also see their journeys hit.

Unite, the union that represents 5,000 workers at seven of the country's main airports including Heathrow, Gatwick, Stansted, Glasgow and Edinburgh, announced on Friday its members were to go on strike in a row over their pension scheme.

The union said workers would stage 24-hour walkouts on January 7 and 14, and a 48-hour stoppage on January 17.