A supermarket chain has apologised after a filling station mix-up led to customers putting the wrong fuel in their cars.

Sainsbury's has blamed a third party supplier for the error which affected 20 drivers at its store in Wantage, when unleaded and diesel fuel were put in the wrong underground tanks.

The customers have been told they will be reimbursed for any damage caused and have been urged to contact the supermarket.

A Sainsbury's spokesman said: "We did experience a technical problem at our Wantage petrol filling station on Wednesday morning and 20 cars were reported to be affected.

"All customers have now been contacted and are being fully reimbursed for the inconvenience caused. The petrol station is now fully open again."

He said the mistake was discovered half-an-hour after the filling station opened at 7am on Wednesday and was then immediately closed down.

The AA advises drivers who have put the wrong fuel in their car not to start their engine as it increases the risk of damage.

Technical specialist Vanessa Guyll said there was a greater chance of long-term damage for diesel cars which had wrongly been filled with petrol.

She said those customers may face a bill of up to £1,500 to replace the fuel pump and to clean out the fuel lines.

Anyone who thinks their car was affected should call Sainsbury's customer careline on 0800 636262.