UK Petrol Held at 150p, Diesel Fell 10p — June 2026 Report

Britain is the odd one out this month. While pump prices have tumbled 10% in the United States, 9% in Canada, and 7% in Australia over the past 30 days (see our U.S., Canada, and Australia reports), the average price of unleaded across the 21 Costco filling stations we track in the UK is 149.4p a litre — just 1.3p below a month ago. Diesel is a different story: it has fallen on almost every day of the window, down 10.2p to 170.9p. The global crude slump is reaching British forecourts — but so far it has arrived almost entirely through diesel.

National averages of posted prices at tracked UK Costco filling stations, p/L. Snapshot taken June 10, 2026 — this article is not updated.

Petrol crept up, then slipped — diesel never stopped falling

The two grades spent the month moving in opposite directions. Petrol rose through late May, peaking at 151.8p on May 29 — days after North American pumps had already broken sharply lower — and only then began easing, giving back 2.3p over the final twelve days of the window. Diesel never wavered: it declined on 24 of 29 days, with the steepest daily falls in the second week of June, for a 10.2p total drop.

Birmingham is the cheapest Costco forecourt in the country

Unleaded moves were modest but one-directional: not a single tracked station charges more than a month ago, and 8 of the 21 cut by more than the 1.5p we treat as noise. Birmingham's 5p cut took it to 142.9p — the cheapest Costco petrol in the UK — while Southampton, at 153.9p, holds the top of the table. The full spread across the network is 11p.

Biggest 30-day unleaded cuts at tracked UK Costco stations, May 12 – June 10, 2026. *Aberdeen's comparison spans 14 days — its price feed is newer.

Posted unleaded prices at tracked UK Costco filling stations, June 10, 2026.

Why petrol is stuck while diesel falls

Both grades are war casualties. When the United States and Israel went to war with Iran at the end of February and the Strait of Hormuz closed, UK pump prices rose for weeks without pause — up roughly 12p on petrol and 25p on diesel in the first three weeks of March alone. From a pre-war 131.7p, the national petrol average kept grinding up to a string of "Iran war highs", peaking at 159.5p on May 28 — its highest since December 2022 — while diesel topped out at 192.1p back in mid-April. Against June 2025, the official DESNZ averages are still up 20% on petrol and 32% on diesel.

Diesel's earlier peak is the clue to its faster fall. Britain is structurally short of the fuel: with Grangemouth out of the refining business since 2025 and only four refineries left, the UK imports roughly two and a half times as much diesel as it produces — much of it from suppliers exposed to the closed strait. That scarcity premium blew the diesel–petrol gap out to about 34p in April, versus under 10p before the war; as ceasefire diplomacy progressed and Westminster eased sanctions on fuel refined from Russian crude in third countries on May 20, that premium began deflating. The gap is back to about 24p nationally — and 21p across Costco's forecourts.

Petrol had no such premium to give back — and its wholesale costs actually rose into late May. The RAC's Simon Williams called May "really quite unusual" — one fuel up, the other down, blaming higher unleaded demand from the United States' summer driving season. At home, the late-May bank holiday brought an estimated 19 million leisure trips, the busiest in two years, landing exactly on petrol's peak. And the UK tax stack mutes every move: 52.95p of duty plus 20% VAT make tax roughly half the pump price, so even big wholesale swings shift the headline number by less, in percentage terms, than they do in North America.

The last factor is who pockets the wholesale fall. The competition regulator's June monitoring report found no war profiteering but put average retailer margins at 11.3p a litre in April — "historically high" — and said it expects wholesale falls to be passed on "rapidly and fully." The RAC's June 8 arithmetic says forecourts still owe drivers about 4p a litre on petrol and as much as 8p on diesel. Costco is ahead of that curve: its petrol average fell 1.3p over a month in which the official national average rose by about 1.1p, and its diesel dropped 10.2p against the national 6.4p.

How Costco compares with the UK average

Costco's members-only forecourts are undercutting not just the national average but the supermarkets that usually set the floor. Against the official DESNZ averagespublished June 9 and the RAC's end-of-May supermarket figures:

UK averages: DESNZ weekly road fuel prices, week commencing June 8, 2026. Supermarkets: RAC average, May 31, 2026. Costco: our tracker, June 10, 2026. Motorway services typically run 15p or more above ordinary forecourts.

That puts Costco unleaded about 8.5p below the UK average and 6p below a typical supermarket, with diesel almost 11p under the national figure — though you need a membership card at the pump, which is the trade-off our UK payment guide covers.

Will UK fuel prices fall further?

Near term, the maths favours drivers: if wholesale holds where it has been, the RAC's owed 4p of petrol and 8p of diesel should keep arriving at the forecourt — and the CMA's next monitoring report, covering June, will show which retailers passed it on. The bigger picture splits on the strait. Fitch's base case has Hormuz reopening around the end of July with Brent sliding toward $70 by September; the EIA assumes shipping resumes in Q3 but not pre-war volumes until 2027; JP Morgan expects crude above $100 for the rest of 2026 even if restrictions lift. Every $10 on a barrel of Brent moves UK pumps by roughly 7p a litre.

One date is already in the diary. The 5p-a-litre duty cut was due to start reversing on September 1 — a penny then, 2p in December — but on May 20 the Prime Minister froze the rise until December 31, 2026 as a war measure ("This is not our war, but… Labour will always protect working people"). What happens after New Year's Eve — the full 5p restored at once, phased, or frozen again — lands in the Chancellor's Autumn Budget. Either way, today's prices sit nowhere near the 2022 records: petrol's 159.5p war peak is still 32p short of the all-time 191.5p.

Frequently asked questions

Costco pump prices are a snapshot observed June 10, 2026 and will differ at the pump today. This site is independent and not affiliated with Costco Wholesale Corporation.