REVEALED: Where to find the cheapest supermarket petrol in Northamptonshire... and the most expensive

Motorists in Wellingborough are being 'ripped off' even more than most over the cost of filling up, according to the RAC.

Supermarket pump prices in the town are up to 5p a litre higher than a few miles down the road in Northampton, Kettering, Rushden and Corby.

The cheapest unleaded in the county, according to price comparison website petrolprices.com on Monday (January 31), is 140.7p a litre at Asda in Kettering — meaning it costs nearly £4 less to fill up an average family car than in Wellingborough.

Experts believe prices are generally lower in towns where Asda has pumps as it is traditionally cheapest among supermarkets.

Rivals such as Sainsbury, Tesco and Morrisons cut their prices at nearby stations in a bid to compete.

In Wellingborough — where there is no Asda — the cheapest fuel is higher than the national average at 145.9p per litre at Sainsbury's.

Cheapest fuel in Northampton is 143.0p per litre at Sainsbury's in Weedon Road.

In Corby the same litre of unleaded is 142.7p per litre at Asda and Morrison's.

Asda is also cheapest among the supermarkets in Rushden at 142.7p.

The RAC has attacked retailers for failing to pass on to drivers drops in wholesale fuel prices.

It says the average price of a litre of unleaded dropped from 147.47p a litre to 145.48p in December when drivers should really have seen prices nearer to £1.35 if retailers played fair instead of taking far bigger margins than normal.

RAC fuel spokesman Simon Williams said: “December was a rotten month for drivers as they were taken advantage of by retailers who rewrote their pump price strategy, costing motorists millions of pounds as a result.

"Their resistance to cutting prices and to only pass on a fraction of the savings they were making from lower wholesale costs is nothing short of scandalous.

"The 10p extra retailers have added to their long-term margin of 6p a litre has led to petrol car drivers paying £5m more a day than they previously would have.

“In the past when wholesale prices have dropped retailers have always done the right thing –eventually – and reduced their pump prices.

"This time they’ve taken advantage of all the talk about ‘higher energy prices’ and banked on the oil price rising again and catching up with their artificially inflated prices.

“The trouble is every extra penny they take as margin leads to drivers paying even more as VAT gets added on top at the end of the forecourt transaction.

"This means the treasury’s coffers have been substantially boosted on the back of the retailers’ action. We urge ministers to push retailers into doing the right thing for consumers."