Fuel prices for fleets

The Department for Energy Security and Net Zero publishes an average UK pump price for diesel and petrol every week, in pence per litre including duty and VAT. THRIVE ingests each release on the Tuesday it appears and keeps the series on the fuel prices page, with a free API. In the week ending 21 September 2026 diesel averaged 195.53p a litre and petrol 172.01p, up 4.81p and 3.87p on the week before, after 190.72p and 168.14p in the week ending 14 September and 186.36p and 164.40p the week before that.

A litre price only matters to a fleet once it becomes a cost per mile. The THRIVE Fleet Cost Index does that conversion every week: the diesel price multiplied by 4.54609 litres to the gallon and divided by a documented representative van economy of 36mpg gives a diesel van cost of 24.69p a mile in the latest week. Set against HMRC's advisory electric rates of 7p a mile for home charging and 15p for public charging, the index stood at 2.63, meaning a diesel van cost 2.63 times as much to fuel per mile as an electric one on a blended charging mix.

For budgeting, the Fleet Fuel Bill Index rebases the diesel price to 100 at its base week, the week commencing 20 July 2026. It stood at 117 in the latest week: a fleet buying the same diesel volume as in July is paying 17% more for it. The weekly move is the figure to watch for cash flow; the index is the one to use for a budget conversation.

Pump prices also feed HMRC's advisory fuel rates, which are reviewed every quarter and set what an employer can reimburse for business miles in a company car without a tax charge. The rates from 1 September 2026 are on the mileage rates and AFR guide, and the AFR archive keeps every quarter on file.