The Transport Secretary Chris Grayling has called for an investigation into "exploitative" motorway fuel prices in a letter to the Competition and Markets Authority (CMA).
Writing to Andrea Coscelli, head of the CMA, Grayling said: "I am concerned that prices which are higher than other forecourts may exploit users in a situation where there is less choice and competition, and discourage motorists from stopping and re-fuelling when, for safety reasons, they should. I would welcome a view from the CMA on whether the three private companies that currently operate the majority of MSAs (motorway service areas) are exercising market power to the detriment of motorists."
In his letter Grayling stated that prices at motorway services could be up to 19ppl more than on forecourts elsewhere. The average price of petrol at motorway services is currently over 17ppl more than the UK average.
He also pointed to RAC figures from 2011, which showed that average MSA petrol prices then were just 7.5ppl higher, showing the "situation had worsened".
The BBC reported a spokesperson for Roadchef who said: "Roadchef does not operate the petrol station forecourts at any of our service areas and does not set the price of fuel."