Petrol and diesel prices at Watson's Centra & Maxol Portaferry

Watson's Centra & Maxol Portaferry, BT221QU.

What it is charging

• Diesel: 191.9p a litre, 6.8p under the national average, filed Thursday 22 October

Unleaded within 5 miles

• Eurospar Killyleagh: 163.9p a litre, 4.6 miles away

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.