Transport problems and floods have wrecked travel plans for millions today 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.
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.
Meanwhile, rail services to Gatwick airport were disrupted by a major signalling problem at Preston Park near Brighton.
Buses were running between Brighton and Haywards Heath/Three Bridges, while no trains were able to run between Brighton and Lewes.
All routes through Blackfriars station in London were being delayed due to signalling problems there and also at Elephant & Castle in south London.
Buses had to replace trains due to flooding on a number of lines
The train problems will continue over the holiday period, as there is likely to be engineering work on the West Coast line.
This will mean there will be no direct services from Euston station in London to Milton Keynes, Birmingham, Manchester, Liverpool or Glasgow on December 23 and 24.
Hourly services will run from Euston via an alternative route (Chilterns) to Nuneaton where passengers will be able to change for services heading to any and all the destinations mentioned above.
Direct services resume on December 27 but with two of the four lines closed up to and including New Year's Eve.
There is engineering work affecting a number of other lines, although Network Rail and the Association of Train Operating Companies have said that the number of replacement buses having to be laid on has almost halved compared with the 2011/12 festive period.
On the London Underground the whole of the Jubilee Line was closed today at the start of services due to a signalling system problem.
The Jubilee Line was up and running with delays by the heart of the morning rush-hour, but other Tube travellers had to contend with severe delays on the Bakerloo Line due to a signalling failure at Paddington in west London.
There will be further chaos on the Underground, as the train drivers' union Aslef is stopping work on Boxing Day in a strike that has already led to the postponement of the London football derby between Arsenal and West Ham United.
Today was the busiest day on the roads as well. Those setting off early faced a number of flooded routes, with the Isle of Wight and Brockenhurst in the New Forest, Hampshire, particularly badly affected.
One lane was closed on the busiest section of the M25 - at junction 15 near Heathrow - due to an accident.
Motorists also had to contend with floods in Reading, Bedford and Henley-on-Thames in Oxfordshire, 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.
The Highways Agency, which is responsible for all of England's motorway and major A-roads, said more than 250 miles of roadworks will have been completed before Christmas.
In addition, a further 57 miles of works will be suspended between today and January 2.
But works remain in place at 19 locations covering nearly 100 miles.
These include the M4 between junctions 10 and 11 at Reading in Berkshire, the M25 at junctions 5 and 6 near Godstone in Surrey, and the M5 between junctions 19 and 21 near Bristol.
The AA said the busiest days on the roads were expected to be today and tomorrow, with 60% of AA members likely to take to the roads over the festive period.
Heathrow is handling 123,000 passengers today, with a further 114,000 departures on Sunday and 88,000 on Christmas Eve.
From today until January 3, a total of 700,000 will be leaving from Gatwick airport.
Approximately 54,000 passengers will take off today from Gatwick, 30,000 will leave through Stansted and Luton will see around 15, 500 passengers heading elsewhere.
British Airways was also having its busiest day of the holiday period today, with 111,000 travellers getting away for the Christmas break.
BA will handle nearly 31,000 passengers on Christmas Day, with the airline carrying nearly 1.6 million in the period up to January 7.
Many of the estimated four million Britons travelling abroad for the holiday set off today.