UK petrol prices: when a cheaper pump is worth the detour

A pump price that is 4p per litre lower saves £2 on a 50-litre fill-up. Whether it saves you money overall depends on the extra fuel you burn getting there and the time the trip takes. For UK drivers comparing petrol or diesel prices, the next useful check is the price at each forecourt and the distance of the entire detour.

What the weekly UK fuel figures can tell you

The UK Department for Energy Security and Net Zero publishes a weekly road fuel price series. It is a national reference for comparing petrol and diesel prices over time. Check the latest release and its date for the current national figures; no price for 5 October is assumed here.

A national average gives context, but it cannot predict the price on a particular pump. Prices may differ between stations, and the price you pay is the one displayed at the forecourt when you fill up. A weekly national figure also cannot establish whether a station is cheaper at the moment you travel.

For a decision about today’s journey, compare prices for the same fuel grade at stations you could realistically use. Check that a listed price is recent, then confirm it on arrival. Petrol and diesel figures should be kept separate: a lower petrol price tells a diesel driver nothing about the cost of their fill-up.

Turn pence per litre into a fill-up cost

Multiply the number of litres you expect to buy by the price per litre in pounds. If a pump displays 150p per litre and you buy 50 litres, the calculation is 50 × £1.50 = £75. At 146p per litre, the same 50 litres cost £73, a £2 difference.

These prices are examples for showing the arithmetic, not reported prices at UK stations. The amount you save changes with the litres you actually buy. A 4p difference saves 80p on 20 litres, £2 on 50 litres or £2.40 on 60 litres. If you only plan a small top-up, even a noticeably lower pump price may produce a modest saving.

Use the litres you expect to purchase, rather than your car’s full tank capacity. A car with a 50-litre tank will not take 50 litres unless it is effectively empty. Your receipt provides the final litres and price if you want to check the result afterwards.

Subtract the cost of reaching the cheaper station

Count the extra distance caused by choosing the cheaper station, including any return journey. Do not count miles you would drive anyway. Estimate the fuel used on those extra miles, multiply it by the price per litre, then subtract that cost from the fill-up saving.

For example, suppose the cheaper station charges 146p rather than 150p per litre, you buy 50 litres, and the detour adds eight miles. The pump saving is £2. At 40 miles per imperial gallon, eight miles uses about 0.91 litres. At £1.46 per litre, that fuel costs about £1.33, leaving roughly 67p before accounting for your time. Real fuel use may be higher in congestion or lower on an easy route.

Time matters even when you do not assign it a cash value. If the detour and queue add 20 minutes, decide whether the remaining saving is worth those minutes to you. A station already on your route may be the better comparison than the cheapest one shown across town.

The practical check is simple: use the latest weekly government figures for national context, then use current forecourt prices, your expected litres and the extra round-trip miles for your own decision. Recalculate if the displayed price or route changes.

Source: UK Department for Energy Security and Net Zero