Rail failures and floods have wrecked travel plans for millions of people on the busiest 24 hours of the Christmas getaway.
A signalling problem in west London meant the Heathrow Express was unable to run and services in and out of Paddington station in London were severely delayed.
Train services near Gatwick airport, in West Sussex, were also affected by a major signalling problem caused by an overnight fire at Preston Park near Brighton. Flooding also caused chaos as a number of rail routes were affected, with surface water causing several accidents and road closures.
The Heathrow Express was cancelled due to a signal failure at Hayes and Harlington in west London, leaving many of the 123,000 departing passengers forced to take the Tube to the west London airport. It also caused delays and cancellations to Paddington services, with those travelling to Cardiff, Reading, Bristol and Bedwyn in Wiltshire among those affected.
Flooding hit a number of train lines, leading to rail replacement buses between Liskeard and Looe in Cornwall as well as Chester and Wrexham General, and services in Derby and Nottingham were also disrupted.
Motorists had to contend with floods in Reading, Bedford, Nottingham, Bromsgrove in Worcestershire, Henley-on-Thames in Oxfordshire and Egginton in Derbyshire, causing long queues on non-flooded roads.
By early afternoon congested spots included the M25 in Essex, while travellers trying to reach Gatwick by road were held up by a sliproad jam on the M23 close to the Sussex airport. Major congestion built up on the M2 in Kent, the M4 in Gloucestershire, the M6 in Warwickshire, the M60 in Greater Manchester and the M77 in Glasgow.
Heathrow was due to handle a further 114,000 departures on Sunday and 88,000 on Christmas Eve. British Airways was also having its busiest day of the holiday period, with 111,000 travellers getting away for the Christmas break.
Many of the estimated four million Britons travelling abroad for the holiday set off on Friday, with popular destinations including the Canary Islands, Tunisia, Cuba and Mexico. Between Friday and January 3, a total of 700,000 will be leaving from Gatwick airport, 320,000 from Manchester, 300,000 from Stansted, 125,000 from Luton, 116,000 from Birmingham and 75,000 from Glasgow.
Many hundreds of thousands will also travel across the English Channel by ferry or through the Channel Tunnel, with 160,000 heading off on the Eurostar.