Nearly three million road journeys are expected to be made on Friday as people begin their Christmas getaway, motoring organisations have warned.
There will be “significant” congestion on major roads, with delays likely on the M25, M6 and M40, the RAC said.
Delays of more than an hour and a half are expected on the M40 southbound.
The RAC’s Matt Dallaway advised drivers to delay their journeys until after 18:00 GMT to miss the busiest time on major roads and motorways.
“Plan your journey, everyone is a hurry to see their loved ones and friends and family, but please think about when you’re going to travel,” he told the BBC.
“Right now until about 18:00 tonight it’s going to be quite busy out there so if you can avoid that, do that – go later or early in the morning.”
Highways England said there were long delays at junction 11A on the eastbound M20, which is the exit for the Channel tunnel, near Folkestone, Kent.
The RAC is expecting delays on the southbound M40 between the M42 in Warwickshire and Junction 8A at Oxford.
It says the number of leisure journeys will peak on Boxing Day, with 6.8 million trips.
Mr Dallaway said: “We’re at this time of year when everyone is frantically trying to get their Christmas presents done, e-commerce is through the roof so there’ll be delivery drivers all over working through to Christmas Eve.
“It’s obviously a lot milder this year… so that will take a lot of people to the roads.”
Meanwhile, Gatwick’s runway has reopened after drones caused the airport to shut for more than a day.