Travellers crowded into air and sea ports and queued in jams on major roads today at the start of a bank holiday weekend expected to produce the hottest weather of the year so far.
Airports had their busiest day of the holiday as they coped with the first of the 1.8 million Britons due to travel abroad over the next few days.
Congestion quickly built up on all major roads, with a spate of accidents and broken-down vehicles adding to the delays.
On the railways, services on South West Trains (SWT) were disrupted after a derailment of a London-bound train outside Windsor and Eton Riverside station just before 6am.
The train remained upright and no-one was hurt, but SWT had to arrange replacement buses in the area for several hours.
Bus replacement will be the order of the day on a number of rail routes tomorrow, Sunday and Monday as dozens of engineering projects are undertaken.
The southern half of the country is set to enjoy the best of the weather, with Saturday and Sunday being dry and sunny.
The north of England and Scotland could get some rain on Saturday but most areas should be fine and dry on Sunday before rain and showers move in on bank holiday Monday.
"We could get temperatures of around 22C (72F) in southern England tomorrow," said Tiffany Curnick, a forecaster with the Press Association's weather company MeteoGroup.
She went on: "It may reach 23C (73F) on Sunday, which would make it the hottest day of the year."
A total of 205,000 passengers passed through Heathrow today and the west London airport will handle around 767,000 customers in the period from today until the end of bank holiday Monday.
Holiday company Travel Counsellors reported that medium-haul destinations such as Egypt and Dubai were popular destinations this year, as well as normal favourites Majorca, Portugal and Turkey.
Travel organisation Abta said Florida was among popular long-haul destinations, while the top five city-break spots were Paris, Amsterdam, Dublin, Rome and New York.
On the roads today, the AA reported heavy traffic on the A303 near Stonehenge where motorists had to compete with large numbers of west-bound caravans.
By early afternoon, there was widespread road congestion. Traffic was particularly heavy on the M25, the M6 in Cheshire, the A46 in Nottinghamshire, the A31 and A35 in Dorset, the A34 in Hampshire, the M5 in the West Midlands and the A1 at Gateshead.
On the railways, the worst day is likely to be Sunday when there are 38 separate engineering work projects taking place.
Passengers on the West Coast Main Line, where a £9 billion upgrade was completed last December, will have to travel on buses between Milton Keynes Central in Buckinghamshire and Birmingham International station.
Among companies having to run buses instead of trains on Sunday - and at other times over the bank holiday weekend - are SWT, Arriva Trains Wales, First Capital Connect, Northern Rail and the Southern train company.Reuse content