Drivers in most parts of the UK are missing out on benefiting from supermarket fuel price wars, according to new analysis.
The AA said retail giants engaged in competitive pump price cuts are primarily restricted to northern England, Northern Ireland and Wales.
But even in those areas, price reductions are only being seen in certain towns.
Supermarket petrol in Greater Manchester last weekend was as much as 13p per litre cheaper in Ashton-under-Lyne – where three superstores in close proximity went “head to head on fuel” – than 10 miles away in Rochdale, the AA said.
There are major differences in average fuel prices across the UK.
In Northern Ireland, diesel was 10p per litre cheaper than in London and south-east England earlier this week.
In Wales, the price was 6p per litre below that in southern England.
AA fuel price spokesman Luke Bosdet said: “Discovering that supermarket petrol or diesel is £5 to £7 a tank more expensive than just 10 miles down the road is guaranteed to leave drivers livid.
“It just doesn’t make sense, particularly when other essentials like bread, milk and eggs are pretty much the same price wherever you go.
“Say, for instance, a supermarket lures you into their store with a voucher offering £6 off a £60 shopping bill.
“To find out that that supermarket clawed back all that saving, and perhaps £1 on top of that, at the pump, compared to a superstore in a neighbouring town, will quite rightly lead to a howl of protest.
“The retailers only get away with it because the fuel price transparency that the Competition and Markets Authority recommended to the Government in October doesn’t yet exist, except in Northern Ireland.”
Average UK petrol prices continued to fall this week, reaching 148.6p a litre on Wednesday, while diesel was down to 170.7p.
Those are falls of 4.4p for petrol and 5.0p for diesel compared with just before Christmas.
The last time pump prices were this low was in mid-February last year for petrol and early March for diesel.