Millions of people are braced for disruption to Christmas Eve getaway journeys due to severe road traffic and strikes decimating train services.
The AA predicted that nearly 17 million cars will be on UK roads on Saturday, leading to severe congestion on major routes.
Pressure on the roads will be raised due to industrial action on the railways.
A walkout by thousands of members of the Rail, Maritime and Transport union (RMT) at Network Rail means trains will stop running early, and some routes will have no services all day.
The RAC and transport analytics company Inrix said the worst Christmas Eve traffic on major roads will be between midday and 1pm.
They highlighted a southbound stretch of the M6 from junction 27 (Chorley, Lancashire) to junction 13 (Stafford, Staffordshire) as the most likely location for long queues.
Many drivers battled a band of heavy rain on Friday which moved north from southern England and Wales to southern Scotland and Northern Ireland.
National Highways said a 10-mile queue built up due to the M25 being closed from junction 11 (Woking, Surrey) to junction 12 (the M3) while standing water was cleared.
Heavy traffic stretched for three miles on the M20 as the westbound section of junction 4 (Leybourne, Kent) was closed after a serious crash on Thursday.
The AA reported “severe congestion” on several motorway stretches on Friday, including the north and west sections of the M25, the M1 around Luton, Bedfordshire, the M4 and M5 near Bristol, the M5 north of Birmingham, the M60 west of Manchester and the M8 near Glasgow.
AA president Edmund King said: “We’re expecting Christmas Day to be quieter with shorter local journeys.
“On Boxing Day traffic will pick up again with approximately 15 million trips as people head out to see friends and family.”
Network Rail said trains will stop running at around 3pm on Christmas Eve.
The early closure means the last departures on some long-distance routes will be before 1pm.
Examples of last train times include 10.45am for Leeds to London, 11am for London to Edinburgh and 12.48pm for London to Manchester.
East Midlands Railway will only run an “extremely limited service” between London St Pancras and Corby, with no trains on routes such as London St Pancras-Sheffield and London St Pancras-Nottingham.
No South Western Railway trains will run on several routes to and from London Waterloo, including Reading, Twickenham and Dorking.
Chiltern Railways will not operate any trains to or from Oxford, or north of Banbury.
No trains operate on Britain’s railways on Christmas Day.
The normal limited Boxing Day schedule has been scrapped due to the strike, while services will start later than usual on December 27.
Christmas is a key period for maintenance work on the railways.
Network Rail planned a £120 million programme of more than 300 projects over the festive period this year.
It said “around 85%” of this work will still go ahead despite the RMT action.
Border Force strikes continue at six UK airports but there was minimal disruption on the first day of the walkout on Friday as armed forces personnel were deployed to check passports.