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Protesters have begun to target motorways in Wales, Essex and Devon, in a demonstration over high fuel prices.
Police have warned there could be "serious disruption throughout the day" as protesters call for a cut to fuel duty.
The action will mainly target three-lane motorways and will see convoys of vehicles driving slowly in two lanes - leaving the "fast" outside lane free.
The protests began in England and Wales shortly after 07:00 BST.
A convoy of about 20 vehicles, accompanied by police cars, left the M4 Magor services near Caldicot in South Wales heading towards the Prince of Wales Bridge across the River Severn into England.
Devon and Cornwall Police said it was aware of a go-slow protest heading northbound from Exeter services.
And a column of about 20 vehicles with hazard lights on joined the London-bound A12.
Fuel prices have risen to record highs in recent weeks with figures from data firm Experian showing the average price of a litre of petrol at UK forecourts had hit 191.4p on Thursday.