Sainsbury’s has raised the stakes in the supermarket price war on forecourts by offering customers spending £30 or more in store or online 10p off a litre of fuel at its 298 filling stations.

The offer – which runs from Thursday 26 February until Wednesday 4 March – means that customers can buy unleaded fuel at less than £1 per litre.

The deal could save a customer driving a family saloon car on unleaded fuel as much as £12.44 compared to prices from the same week last year. This is based on the average cost of filling up a car with 40 litres of unleaded petrol. The saving is available to customers shopping in supermarkets and convenience stores – and online customers will also benefit, receiving a coupon with their grocery delivery.Plunging world oil prices had prompted leading supermarkets to cut the cost of their fuel, although prices have recently started rising again.

Analysts believe the reduced cost of filling up a car with fuel will act like a tax cut, boosting real incomes and discretionary consumer spending.

The RAC motoring group welcomed the move by Sainsbury’s. Its fuel spokesman Simon Williams said: “Motorists will have noticed pump prices edging up in recent weeks after reaching a five-year record low as a result of the recovery in the price of Brent crude and subsequent increase in wholesale fuel prices”.

Even so, families are paying on average 20p per litre less for unleaded this year compared to this point last year – and 30p less when compared to 2013, the RAC said. “Today’s new offer from Sainsbury’s will mean thousands of motorists are able to enjoy fuel at prices close to or possibly even below £1 per litre” Williams added. Fuel makes up such a large proportion of the average family budget that anything that helps keep the cost down is to be welcomed”.

Sainsbury’s has spent £150m in price cuts over the last few months, lowering the regular price of thousands of lines across its grocery business.