Motorists are set to face the worst bank holiday traffic in a decade as soaring temperatures, rail disruption and a spike in late holidays cause “carmageddon” on roads around the capital.
Twice as many vehicles could take to motorways between Friday and Monday compared with a normal weekend, experts have said.
The huge number of cars on the roads could cause tailbacks of up to two hours on the busiest routes such as the M25, M27, M5 and M6.
Almost 248,000 people – around 25 per cent more than on a normal day - are expected to fly in and out of Heathrow on Friday with large numbers of families preparing to take a late summer holiday before the new school year, which starts next week in some areas.
Travellers have been warned that queues of up to 90 minutes could build between junctions 9 and 21 of the M25 affecting journeys to both Heathrow and Gatwick.
Network Rail plans to carry out 940 engineering projects over the weekend as part of a £30 million upgrade resulting in a partial shutdown of the UK’s train network and causing further chaos on the roads.
Trains between London Paddington and south Wales will be severely disrupted as the Severn Tunnel is closed for six weeks for repairs.
Other services affected include Southeastern, South West Trains, Greater Anglia, Virgin Trains west coast, London Midland and Great Northern.
Highways chiefs are preparing to lift or complete more than 370 miles of roadworks by the end of this week, but have been warned that the emergency measure would fail to prevent gridlock.
Inrix, which supplies traffic data, said drivers "could face the worst bank holiday congestion in a decade".
Greg Hallsworth, a UK traffic analyst, told the Times: "A perfect storm of conditions will lead to increased traffic as 'carmageddon' blights the long weekend.
“With some good weather forecast and potential rail disruption, holidaymakers could find roads gridlocked far more than usual. We could see delays of more than 120 minutes for some of the worst affected roads this weekend."
Motorists have been urged to plan ahead in the wake of another heatwave with forecaster predicting highs of 29C in London and the southeast.
Drivers are advised to carry lots of water with them and keep cars cool.
