Motorists are being warned to expect severe congestion, with the AA issuing its first ‘amber traffic warning’ for Friday and Saturday.
Congestion is expected to peak between 11am and 3pm on both days.
This is due to a combination of early changeover days for holiday lets during the summer school holidays in England and Wales, a rail strike, the Commonwealth Games in Birmingham and the start of the season Football League in England.
Roads approaching Dover and the Folkestone Eurotunnel terminus are expected to be busy, as are those serving Devon and Cornwall, including the M5, A303 and A30.
The south-west and west sections of the M25, the M4/M5 Bristol junction and the M6, M42, M1 and M62 are also vulnerable to congestion this weekend.
Jack Cousens, head of roads policy at the AA, said: “With the bank holiday changeover day starting on Friday mixed with rail strikes and a big sports weekend, we are concerned that drivers will experience delays to the whole network, with southern England particularly vulnerable.
“All eyes will be on Dover and Folkestone but we believe changes have been made over the course of the week and we’ll be crossing our fingers for a smoother trip across the Channel.
“Breakdowns can make traffic jams worse and last weekend we saw an increase in breakdowns where vehicle checks had not been carried out before leaving.
“Spending 10 minutes checking tires and fluid levels before setting off can make a huge difference in helping people get to their destination.”
RAC traffic spokesman Rod Dennis said: “Analysis of Inrix traffic data shows long delays are expected on Friday, Saturday and Sunday on the M25 between Bromley and Dartford Crossing, as well as the ‘A303 westbound towards Devon.
“Over the weekend, the M5 southbound near Bristol and the M25 clockwise between the M23 and M40 junctions are also likely to see some long queues.
“Drivers using these routes, as well as those crossing Kent who may be affected by traffic bound for the Port of Dover, should prepare for a longer journey and not rely on the earliest estimated time of arrival given by your sat navs.
“Dial early in the morning is the best way to avoid traffic.”
Tens of thousands of families saw the start of their journeys across the Channel ruined last weekend as roads approaching Dover were blocked, causing delays of several hours.
This was attributed to a shortage of French border officers and a serious accident on the M20.
The operation was much smoother on Friday morning, with P&O Ferries saying there were “no queues at border controls and traffic is flowing freely through the port”.
Port of Dover chief executive Doug Bannister said on Thursday that French border controls will be “fully resourced”, which will make a “fundamental difference”.
The port expects to receive around 140,000 passengers, 45,000 cars and 18,000 cargo vehicles between Thursday and Sunday.
National Highways, which manages England’s motorways and major A roads, said: “Drivers traveling in and around Kent are advised to plan ahead as this weekend is likely to be very busy.
“Operation Brock contraflow remains in place on the M20 and is part of a series of measures to improve Kent’s resilience and ensure the smooth flow of traffic across the region in the event of disruption to services across the Channel Hose”.