Fuel price protests are set to make traffic jams even worse during what is expected to be the busiest summer getaway in at least eight years.
Avon and Somerset Police warned motorists that “slow-moving roadblocks” are planned on parts of the M4, M5, M32 and A38 on Friday morning.
An image posted on Facebook group Fuel Price Stand Against Tax suggests demonstrations will be held “nationwide”, including in Birmingham, Cardiff, Liverpool, London and Manchester.
With most schools in England and Wales breaking up for summer this week, the RAC said an estimated 18.8 million leisure trips are planned in the UK between Friday and Monday.
That is the most since the company began tracking summer getaway numbers in 2014.
Superintendent Tony Blatchford of Avon and Somerset Police urged drivers to consider “alternative travel plans” due to the pump price protests.
He said: “Our protest liaison team has been engaging with the organiser so we can inform the public of the likely disruption and help to minimise it.
“Nevertheless, drivers can expect journey times will likely be longer than normal, especially on motorways, which often tend to be at their busiest at this time of year.
“We advise motorists to consider any alternative travel plans available and ensure they are suitably prepared in case they are delayed.”
Fuel price protests on July 4 led to 12 people being arrested on the M4.
The first stage of Friday’s action in the South West will see vehicles travel north on the M5 between Bridgwater and the Almondsbury Interchange from about 8.45am, then east along the M4 and to Junction 1 of the M32.
The convoy is expected to leave the motorway and stop “for a period of time” before completing the same route in reverse, arriving back in Bridgwater “in the early afternoon”, police said.
A second group of protesters is planning to drive slowly to the Shell petrol station in Bristol Road, Bridgwater.
“They are expected to block the forecourt during the morning,” according to police.
Figures from data company Experian show the average price of a litre of petrol on Wednesday was 187.5p, while diesel was 196.1p.
Long queues are likely at the Port of Dover (Gareth Fuller/PA)
Transport analytics company Inrix believes the M25 – London’s orbital motorway – could see some of the worst jams due to the summer getaway, singling out the stretches between Bromley and the Dartford Crossing; Maple Cross and the M3; and the M23 to the M40.
The A303 near Stonehenge, Wiltshire, the M4 between Cardiff and Newport in south Wales, and the M5 south of Bristol are also likely to see queuing traffic.
Climate protesters caused major disruption on Wednesday by climbing onto signs above the M25.
There are also likely to be long queues at the Port of Dover again on Friday.
Travellers were forced to queue for up to three hours on Thursday to complete border control and check-in.
On Thursday afternoon, a spokesman for the port said: “As a result of high demand and earlier capacity issues at the border, the port system is working hard to catch up and to get everyone through as quickly as possible.
“Passengers will be placed on the first available sailing and will be away on their holidays shortly.”