Where is the cheapest supermarket to fill up in Northamptonshire — and the most expensive?

Motorists in Wellingborough could be paying up to £4 EXTRA every time they fill up than just eight miles up the road in Kettering.

The average price of fuel at the 'big four' supermarkets nationally is around 109.9p for unleaded and 113.9p for diesel.

Yet Morrisons, Sainsbury's and Tesco are all charging way above that in Wellingborough, less in Northampton and Corby and a LOT less in Kettering as prices vary widely across the Northamptonshire.

And RAC's fuel expert Simon Williams reckons the postcode lottery for fuel prices is mostly down to having an Asda close by, adding to competition.

Mr Williams said: "Asda is known to be very competitive on price.

"Other supermarkets try to compete with them in towns where there is an Asda then make up for it by charging more elsewhere.

"Hence you get such a difference in price between towns.

“We badly need greater transparency in fuel retailing so that drivers pay a fair price for their petrol and diesel wherever they choose to fill up.”

Comparison site petrolprices.com checks pump prices daily.

Their latest research shows Kettering prices are even cheaper than nine miles away in Corby, where there is also an Asda.

Kettering supermarkets charging between 106.7p and 108.9p per litre for unleaded. The cheapest unleaded in Wellingborough is Morrisons' 109.9p per litre while Tesco and Sainsbury both charge 110.9p.

In Northampton and Corby, supermarket pump prices are around 109.9p.

Drivers in Kettering can get their diesel between 110.7p and 112.9p per litre yet the same fuel costs around 112.9 or 113.9p per litre in Northampton and Corby — and a whopping 117.9p per litre at Tesco in Wellingborough.

The average family-sized car with a 55-litre fuel tank will cost an extra £3.85 to fill up at Asda in Kettering compared to Tesco in Wellingborough.

Morrisons, Asda and Tesco all announced back in May that the cost of unleaded would fall to less than £1 a litre and less than £1.05 for diesel.

Since then pump prices have risen by about 6½ per cent in Kettering — but ten per cent in Northampton and Wellingborough.

We contacted Sainsbury's, Morrisons and Tesco for comment regarding their fuel prices.

The only response was a spokesman from Sainsbury's who said: “We price our fuel locally and always aim to be competitive.”