A severe traffic warning has been issued as millions of drivers embark on Christmas getaway journeys.
The RAC, which expects 7.9 million leisure journeys to be made across the UK on Friday and Christmas Eve combined, published the alert for a stretch of the M25.
Congestion on the clockwise section between junction seven for the M23 and junction 16 for the M40 is expected to peak at 12.30pm on Friday, when delays of around 50 minutes are likely.
Other roads where long queues are expected on Friday include the M60 near Manchester, the M6 in north-west England and the M40 in Oxfordshire.
Junction four of the M20 westbound in Kent remains closed on Friday morning after a serious crash on Thursday.
National Highways said vehicles are being diverted on to exit and entry slip roads, causing three miles of congestion and delays of at least 45 minutes.
Drivers in Wales and southern England are also battling with heavy rain, which the Met Office said will spread northwards to reach southern Scotland and Northern Ireland during Friday afternoon.
Pressure on the roads ahead of Christmas Day is being exacerbated by industrial action.
Many people are expected to switch to road transport due to thousands of members of the Rail, Maritime and Transport (RMT) union at Network Rail walking out from 6pm on Christmas Eve, causing train services to finish at around 3pm that day.
An overtime ban is also causing major disruption to services by a number of operators on Friday, including Chiltern Railways, East Midlands Railway and South Western Railway.
Transport analytics company Inrix expects journey times by road to be around 14% longer compared with the same period last year.
RAC spokesman Rod Dennis said: “We’re expecting to see lengthy delays on parts of the M25 today as Christmas getaway and end-of-the-week commuter traffic combine.
“We advise drivers, if possible, to avoid these roads around this time or delay their trips until after 7pm this evening when traffic is predicted to be lighter.”
He urged motorists to carry out pre-journey checks on their vehicle before setting off, to reduce the chance of suffering a breakdown.
National Highways said almost 98% of England’s motorways and major A-roads will be fully open until the end of January 2 due to it completing and lifting roadworks.
