Drivers are being warned to expect long delays on popular routes during the Platinum Jubilee bank holiday period as nearly 20 million getaway journeys are planned.
The RAC estimated that 19.5 million leisure trips by road will take place between Wednesday and Sunday.
A survey of 1,460 drivers’ travel plans indicated that Friday is likely to be the most congested day on the roads as day-trippers combine with families returning home from half-term breaks.
Traffic information supplier Inrix advised drivers to set off either before 6am or after 3pm to avoid the worst of the traffic.
The M25 anticlockwise from Junction 17 at Maple Cross Interchange, Hertfordshire to Junction 12 at Thorpe Interchange, Surrey has been highlighted as a likely congestion hotspot.
Another is the A303 running past Stonehenge, Wiltshire, which is a popular route for holidaymakers travelling towards the South West.
Some 37% of respondents to a separate RAC poll said they will not be driving long distances over the weekend.
Of those people, 11% attributed this to high fuel prices.
RAC traffic spokesman Rod Dennis said: “Drivers clearly see a double bank holiday this close to the summer as a gift with so millions eager to make the most of it – although many appear keen to keep their car journeys short, perhaps mixing a daytrip or two with a Jubilee celebration at home.
“The fact the bank holidays coincide with the end of half-term in many places has the potential to put some extra pressure on the road network, so planning a journey carefully is important to beat the worst of any queues.”
He urged drivers to carry out essential checks on their vehicles before setting off, such as making sure oil, coolant and screen wash levels are correct, and tyres are properly inflated and free from damage.
“A bit of TLC now could make the difference between a straightforward trip and one beset by a breakdown,” he added.
UK airports will also be busy with more than 10,000 flights departing between Thursday and Sunday, according to aviation data firm Cirium.
That is a three-fold increase on the same period last year, when the UK’s coronavirus travel restrictions remained in place.
Thousands of families have seen their half-term holidays disrupted as easyJet cancelled more than 200 flights to or from Gatwick over a 10-day period.
Tui has also axed a number of flights.
Network Rail normally carries out widespread engineering work during bank holidays, but nearly all major lines will remain open during the Jubilee celebrations.
Chief executive Andrew Haines said: “We are really pleased to say that all routes into London’s major stations will be open across the Queen’s Platinum Jubilee bank holiday weekend.
“We know that demand will be high as people travel into the capital to celebrate this special occasion and our station staff will be on hand to welcome passengers and help them with their journeys.
“Of course, we are still carrying out hundreds of important projects to upgrade the railway, but the majority of these will have no impact on passenger or freight services.
“As ever I’d like to thank the countless railway staff who will be out delivering upgrades or who will be working hard to keep services running for passengers.”