New research by Traffic Watch shows pre-Christmas leisure traffic will peak on Christmas Eve when 1.87m separate getaway auto journeys will be taken, but in reality today (Friday) is likely to be the most congested on the roads as commuter traffic mixes with an expected 1.25m leisure trips.
RAC traffic spokesman Rod Dennis said: "Things tend to get worse on the last working day before Christmas, with 'Frantic Friday" this year falling on December 22.
It is adding nearly 30,000 extra seats to services between Monday and January 2, with Christmas Day bookings up by almost a quarter on past year. It's tricky to avoid'.
From Friday afternoon onwards, drivers should expect long queues, traffic experts have warned, with the RAC adding that drivers should avoid long journeys "if they possibly can".
Dr Cookson said the M25 is "right at the top of the list" for long queues, warning that "it doesn't matter which way you're going around it".
Elsewhere in the UK, Dr Cookson predicted that the M6 between Merseyside and Staffordshire, M1 and M4 will be "incredibly busy".
It estimates that 11.5 million leisure trips will be made by vehicle between December 17 and Christmas Eve, but this will be eclipsed by the 17.5 million taking place between Christmas Day and New Year's Day as people take advantage of post-Christmas sales at shops.
Highways England's customer service director Melanie Clarke said: "We're doing everything we can to make journeys as smooth as possible this Christmas and that's why we're keeping 99% of the road network we manage free from roadworks".
WENNTraffic has already built up as Kent's Bluewater shopping centre
The "roadworks embargo" will be in place on motorways and major A roads from 6am on Friday until 12.01am on January 2.
Some 260 engineering projects on the railway will also disrupt journeys.
Millions of Christmas shoppers are expected on city high streets today to grab last minute gifts.
The RAC says a total of 11.5 million leisure journeys will take place in the run-up to Christmas, but this will be eclipsed by the 17.5 million set to take place between Christmas Day and New Year's Day.
Aside from the roads, many of Britain's mainline train routes will be partially shut as Network Rail carries out its biggest ever Christmas investment programme.
Great Western Railway is urging passengers to complete journeys by Saturday "at the latest" as London Paddington will be closed between Christmas Eve and December 27.
Passengers travelling between London and Glasgow during this time are advised to go via Edinburgh, adding around an hour to journeys.
Coach operator National Express is running its largest ever Christmas schedule to meet increased demand from key locations such as Bournemouth, Cardiff, Leeds, Edinburgh, Portsmouth, Bristol, Glasgow and Manchester.
Ed Sheeran Christmas number one for 2017
He was the chart-topper last week and faced stiff competition from rapper Eminem and his track River, which featured Ed. It re-entered the chart this year as this Christmas day marks the one year anniversary of George Michael's death.
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