Drivers are being ripped off by "greedy" motorway service retailers, it is claimed.
Motorists pay far more for items such as petrol, food and drink than they would at high street outlets.
What Car? says it found a WH Smith motorway services outlet that was charging consumers a 91% motorway mark-up over its high street outlets on a 750ml bottle of water.
It adds that Marks & Spencer also charges "inflated prices" in its motorway shops, including a 25% increase on a bottle of water, 16% on a sandwich and 15% on a large sausage roll.
Also, Burger King charges 12% more on the motorway than it did in its high street restaurants.
The survey shows that fuel is also more expensive at motorway services, with drivers having to pay an average motorway levy of 5.2% for unleaded fuel and 3.4% for diesel.
Consumers filling their fuel tank at motorway services will pay on average £77.00 more per year than they would if they filled up off the motorway.
While it costs retailers more to transport goods to service stations, What Car? editor-in-chief Steve Fowler maintains: "It is unforgivable for retailers to take advantage of motorists in such a brazen manner.
"With fuel prices at an all-time high, the 5.2% average motorway fuel mark-up is hard for consumers to fund, and a 91% mark-up on a bottle of water is utterly unacceptable.
"We suggest that all motorway users plan their journeys carefully and try to avoid using such greedy retailers as much as possible."
Further reading/Key links
Drive down travel costs: Cheap Petrol & Diesel, Cheap Car Insurance, Cheap UK Travel, Cheap Train Tickets
Cut shopping costs: High Street Haggling, Cheap Online Shopping