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.
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 day trip 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 screenwash 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.
