Fair Fuel UK has criticised retailers who have been slow to pass on the reduction in fuel duty by 1p a litre at the petrol pump.
Chancellor George Osborne's decision to postpone next month's increase introduce a fuel stabiliser was widely welcomed by weary motorists.
But reports have emerged that some garages are failing to pass on the savings to drivers struggling to cope with high petrol and diesel costs.
Prices at a BP garage at the Moto Services on the eastbound M2 between junctions 4 and 5 for Gillingham, Kent, had remained the same at 142.9 for regular unleaded and 147.9 a litre for regular diesel.
Lynne Beaumont, a spokesman for Fair Fuel UK, said: "That is just greed and it is appalling that the retailer is getting away with that.
"People need to think more carefully and ask themselves whether they are being taken for a ride by garages charging such prices.
"We pay more duty than anyone else in Europe and that's not right, so it's important that we continue to fight to bring prices down."
A member of staff at the BP garage in Kent declined to comment on the pricing.
A BP spokesman said that the company does not set fuel prices at that particular garage.
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