Mfg Gretna (msa), DG16 5HQ. A motorway service area, where you have no choice.
What it is charging
Unleaded: 185.9p a litre, 14.2p over the national average, filed Friday 23 October
Unleaded within 5 miles
Crossways Filling Station: 170.9p a litre, 1.4 miles away. 15.0p a litre cheaper: saves £8.25 a tank, and costs about 54p of fuel to get there and back. Worth the trip.
Gem Longtown: 170.9p a litre, 4.5 miles away. 15.0p a litre cheaper: saves £8.25 a tank, and costs about £1.74 of fuel to get there and back. Worth the trip.
On a 55-litre tank at 40mpg. The distance is straight-line rather than by road, so a real trip is longer than the one costed here.