Last month Britain was the odd one out — petrol barely budged while North America tumbled. This month it caught up. Across the 21 Costco filling stations we track in the UK, the average price of unleaded is 142.5p a litre — down 6.4p, or 4.3%, from 148.9p a month ago, and diesel has fallen even harder, down 14.0p (−8.2%) to 155.5p. The wider market tells the same story: the RAC says UK diesel posted its biggest monthly fall on record in June, and petrol its seventh biggest. Unlike the sharp bottom-and-bounce we logged in the U.S. and Canada this week, Britain's slower-moving forecourts are still gliding down — but that is exactly why the early-July crude rebound has not reached them yet.
| Grade | June 11 | July 10 | 30-day change |
|---|---|---|---|
| Unleaded petrol | 148.9p | 142.5p | ▼ 6.4p (4.3%) |
| Super unleaded | 159.9p | 153.3p | ▼ 6.6p (4.1%) |
| Diesel | 169.4p | 155.5p | ▼ 14.0p (8.2%) |
National averages of posted prices at tracked UK Costco filling stations, p/L. Snapshot taken July 10, 2026 — this article is not updated.
Petrol finally joined diesel on the way down
In June, petrol at Costco slipped barely a penny while diesel did all the falling. Over the past 30 days both grades declined in near-parallel lines: petrol shed 6.4p and diesel 14.0p, and — unlike North America — neither has turned back up yet. Petrol reached its low of 142.4p on July 7and has sat flat since; diesel bottomed at 155.4p on July 8. The diesel–petrol gap, blown out to about 34p at the war's April peak, is back to 13p across Costco's forecourts.
Haydock is the cheapest Costco forecourt in the country
Every tracked station is cheaper than a month ago. Haydock's 10p cut took it to 137.9p — the cheapest Costco petrol in the UK — while Reading gave back 8p and Coventry, Glasgow, and Edinburgh 7p each. Aberdeen, at 146.9p, now holds the top of the table; the full spread across the network is 9p.
| Filling station | Unleaded now | 30-day change |
|---|---|---|
| Haydock | 137.9p | ▼ 10.0p |
| Reading | 143.9p | ▼ 8.0p |
| Coventry | 144.9p | ▼ 7.0p |
| Glasgow | 141.9p | ▼ 7.0p |
| Edinburgh | 141.9p | ▼ 7.0p |
Biggest 30-day unleaded cuts at tracked UK Costco stations, June 11 – July 10, 2026.
Cheapest unleaded right now
| Station | Price |
|---|---|
| Haydock | 137.9p |
| Oldham | 138.9p |
| Birmingham | 139.9p |
| Thurrock | 139.9p |
| Manchester | 140.9p |
Priciest unleaded right now
| Station | Price |
|---|---|
| Aberdeen | 146.9p |
| Stevenage | 145.9p |
| Chester | 144.9p |
| Coventry | 144.9p |
| Southampton | 143.9p |
Posted unleaded prices at tracked UK Costco filling stations, July 10, 2026.
Why Britain caught up — and why diesel led
Both grades are war casualties working off the same spike. When the United States and Israel went to war with Iran at the end of February and Iran closed the Strait of Hormuz, UK pump prices rose for weeks — about 12p on petrol and 25p on diesel in the first three weeks of March alone — peaking near 158p on petrol and 192p on diesel in mid-April. The unwind that reached North America first has now fully arrived here: the June reopening of the strait pulled Brent down toward $72, and the RAC says the Iran-war inflation shock is rapidly unwinding at the pump.
Diesel led because it rose furthest. Britain imports far more diesel than it refines, much of it from suppliers exposed to the closed strait, so the war blew the diesel–petrol premium out to record width — and it is that premium deflating that shows up as June's record monthly drop and our 14p Costco fall. Petrol had less to give back, which is why its decline, though real this month, is smaller. Britain's forecourts also simply move slowly: heavy fixed tax — duty plus 20% VAT is roughly half the pump price — mutes the percentage effect of any wholesale swing, and pass-through here lags the wholesale market by up to a fortnight.
A caution before you bank the next few pence
That fortnight lag cuts both ways. In the U.S. and Canada, crude's early-July rebound — on doubts about the U.S.–Iran ceasefire — has already pushed pump prices back up. UK forecourts have not felt it yet, which is why Britain's lines are still sloping down while North America's have turned. If the rebound holds, the slide you see here stalls next; if the ceasefire steadies and crude resumes falling, a little more relief is still owed.
How Costco compares with the UK average
Costco's members-only forecourts are still undercutting the national pump. Against the official weekly road-fuel averages for the week commencing July 6:
| Fuel | UK average | Costco | Costco vs UK |
|---|---|---|---|
| Unleaded petrol | 149.8p | 142.5p | −7.3p |
| Diesel | 164.8p | 155.5p | −9.3p |
UK averages: GOV.UK weekly road fuel prices, week commencing July 6, 2026. Costco: our tracker, July 10, 2026. Motorway services typically run 15p or more above ordinary forecourts.
That puts Costco unleaded about 7p below the UK average, with diesel more than 9p under the national figure — though you need a membership card at the pump, the trade-off our UK payment guide covers.
Will UK fuel prices fall further?
Near term, Britain's lag means a little more of the wholesale fall is probably still in the post — provided crude behaves. Beyond that it hinges on the strait: the EIA assumes Hormuz shipping keeps recovering toward pre-war volumes into 2027, which would keep Brent easing, while the early-July rebound is the standing reminder that a shaky ceasefire can reverse it overnight. 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 fuel-duty cut, frozen through 2026 as a war measure, is due to start reversing from January 2027 — 3p in January, another 2p in March — restoring the main rate to 57.95p and adding those pennies straight onto the pump. Even so, today's prices sit well below the 2022 records: petrol's 142.5p Costco average is more than 45p under the all-time high.
Costco pump prices are a snapshot observed July 10, 2026 and will differ at the pump today. This site is independent and not affiliated with Costco Wholesale Corporation.
