Britons heading for Brussels endured travel disruption today as the Christmas getaway began in earnest.
A 24-hour strike by Belgian workers meant London to Brussels trains run by Channel Tunnel high-speed rail company Eurostar had to start and finish at Lille in northern France.
A limited coach service was operating between Lille and Brussels. Eurostar's London-Paris services were operating normally.
Back in the UK, with abnormally mild weather predominating, today and tomorrow were expected to be the busiest days of the festive period on the roads.
The AA has said it expects up to 18 million cars will take to the roads over the holiday period.
It predicted that getaway traffic in the run-up to Christmas was likely to be heavy on major routes, including the M1 in Buckinghamshire and Bedfordshire, the M4 between London and Newbury in Berkshire, the M25 around London, and the M4 and M5 in the West Country.
The Highways Agency, which is responsible for England's motorways and major A-roads, said it planned to complete more than 500 miles of roadworks before Christmas while a further 60 miles will be suspended from Friday until January 3.
In total, 118 sets of roadworks should be finished by Christmas, with works staying in place at 26 locations, including a 32-mile section of the M1 near Luton in Bedfordshire.
Other areas where works will still be in place include a 15.5-mile section of the M25 near St Albans in Hertfordshire, a section of the M4 near Wokingham in Berkshire and a 12-mile section of the M62 near Huddersfield in West Yorkshire.
For those taking domestic train services in the UK over Christmas and New Year, buses are replacing trains on some rail routes.
However rail chiefs have said that the number of replacement buses has halved compared with the 2010/11 festive period, and around 54,000 more trains will be running this year compared to last.
As much as £109 million of work is being done on the rail network over Christmas and the new year, with projects including work at Birmingham New Street station and at Reading station in Berkshire.
Travel will be free on Tubes and London buses from 11.45pm on New Year's Eve until 4.30am on New Year's Day.
A total of 4.25 million Britons are due to travel overseas between December 16 and January 3, compared with just under four million for the festive period in 2010/11.
This year, around 1.7 million festive travellers will be leaving from Heathrow airport, 425,000 from Stansted, 750,000 from Gatwick and 210,000 from Luton.
Also, 340,000 will be departing from Manchester airport, 165,000 from Birmingham and 120,000 from Glasgow, while many thousands will be crossing the English Channel or travelling through the Channel Tunnel.
Passengers using Heathrow over the festive period are expected take 6,000 tonnes of luggage each day - equivalent to the weight of 20 jumbo jets.
Heathrow's most popular destinations this Christmas are New York, Dubai, Dublin, Amsterdam and Paris.
Popular destinations for Britons travelling abroad include the Canary Islands, Cuba and Mexico, while top city break destinations include Paris, Rome, Dublin, New York and Reykjavik in Iceland.
At the Port of Dover this morning, officials said all services with P&O Ferries to Calais and DFDS to Dunkirk were running normally with space available.