Drivers are being warned to expect delays on roads from Monday as the Christmas getaway begins, with 60 per cent of trips crammed into the three days before 25 December.
Motorists are expected to make 21 million leisure trips between Monday and Christmas Eve, according to the RAC.
Around 13.5 million journeys by car are predicted from Friday until Christmas Eve, an increase of 20 per cent on the same period last year.
Congestion is likely to peak on Friday as drivers heading away for Christmas join commuters and business traffic behind the wheel.
Train travellers also face disruption as Network Rail carries out engineering work.
Paddington will be shut from Christmas Eve until 27 December. There are no direct National Rail or Heathrow Express services from the station to or from central London to or from Heathrow from 24 to 27 December. The Elizabeth line will run between Ealing Broadway and Heathrow Airport on 24 and 27 December only.
meaning no trains to Heathrow Airport from there on those days, while King’s Cross will be closed on Christmas Eve.
RAC spokeswoman Alice Simpson said: “Since Christmas falls on a Monday this year, there’s no need for drivers to use annual leave for getaway trips as they can travel over the weekend before.
“For that very reason, our research suggests these days will be the busiest times to drive, so we urge people to set off as early as possible on Saturday and Sunday.”
Transport analysis company Inrix warned of “daily delays of around 40 minutes” were likely between Friday and Christmas Eve on the M25 clockwise west of London.
The worst queues will be on the M25 clockwise between junction 7 (for M23/Gatwick airport) and junction 16 (for M40/Birmingham) on Friday, Inrix predicted.
Drivers heading anti-clockwise between junction 17 (Rickmansworth) and junction 12 (for M3) on the same day are also being warned to prepare for hold-ups.
Other motorway stretches identified as potential hotspots include the M1 north from Woburn, Bedfordshire to Daventry, Northamptonshire and the M6 south from Wigan, Greater Manchester to Stafford, Staffordshire.
During the weekend before Christmas, between 12pm and 2pm is expected to be the busiest time to travel on the roads.
Bob Pishue, INRIX transportation analyst, said: “On average, drivers could see travel times up to 20 per cent longer this holiday season, while travellers around Greater London could experience more than double typical drive times.
“Our recommendation is to avoid peak commuting hours and use traffic apps to minimise holiday travel traffic frustrations.”
National Highways says it will remove more than 1,000 miles of roadworks on England’s motorways and A-roads by 6am on Tuesday.
That means more than 98 per cent of its network will be free of roadworks until January 2.
The best time for motorists to head off is before 11am or after 6pm to reduce the chance of being stuck in long queues.
Drivers are advised to check fuel, oil, tyres, coolant, electrics and screenwash before making a long journey.
On the railways, an engineering project near Southampton will cause disruption to services, as will work to build the new Cambridge South station.
No trains will operate on Christmas Day, with a very limited service running on Boxing Day.
Network Rail says 96 per cent of the rail network will remain open as normal but it is carrying out “some significant projects”.
It added that engineering work is planned to “target the quietest times” to minimise disruption.
Heathrow Airport expects 6.5 million passengers will travel through its terminals this month, with tens of thousands departing on Christmas Day.