Drivers were charged 30p per litre less when filling up at a supermarket petrol station after a fuel pump error.

Lucky motorists noticed that despite signs on the road advertising unleaded for 145.7p and diesel for 148.7p at the Asda store in Gillingham, the pumps were issuing fuel at bargain prices.

Petrol prices have increased dramatically recently but the motorists were fortunate to discover on Monday that the supermarket was dispensing fuel at prices many have not seen for several months.

One driver arrived at the Pier Road store at about 5.15pm yesterday and was charged just 115.7p per litre to fill up – 30p less than the advertised rate on the tower on the main road.

Brad Harper said: "After I had put my card in the reader at the pump, I noticed the price of both petrol and diesel was being advertised at bargain prices.

"I was intrigued to know whether this was being advertised on the tower in Pier Road but it was showing 145.7p for unleaded and 148.7p for diesel.

"I used pump six and looked at the one next to mine which showed the same.

"It was very lucky indeed."

Meanwhile, drivers filling up with diesel were charged 125.7p – 23p lower than the digital sign on the road side.

Prices were back to normal today and being issued at the same as the entrance sign showed at 145.7p for unleaded and 148.7p for diesel which is in line with overall average prices for the area.

The latest AA fuel price index for October shows the average price of unleaded rose from 135.2 per litre to 141.4p per litre compared to September. Diesel increased from 136.9p to 144.9p per litre.

The last time prices were as low as drivers at Asda paid last night was in March for diesel and in February for unleaded, according to the AA figures.

A spokesman for Asda said: "We apologise that due to a technical issue with our systems following a planned update, the price of fuel on our advertising board was different to that shown on the pump at our Gillingham Pier store yesterday evening.

"This issue has now been resolved and we would like to reassure customers that the price shown on the pump will always be the price that our customers will pay."

It follows another fortunate break for motorists after the Tesco store in Sheerness was forced to honour reduced prices when rats gnawed through a data cable and changed the prices on the advertisement sign just off the forecourt.

Staff were unable to change the prices due to the technical problem and the station was unable to take contactless payments as a result.