Hampton Magna resident Carole Johnson believes criminals used equipment at the Shell garage in Hatton to clone cards belonging to her and her son Nicholas.

Both used cards to pay for petrol and learned days later that withdrawals had been made in their names from machines in Australia.

Now Mrs Johnson is concerned others might fall prey to the thieves.

She said: “I don’t know how they have done this. It is a bit concerning that other people might have used their credit cards at the garage and not known about it.”

In both cases, three cash withdrawals were made. The money has been refunded to Mrs Johnson and her son but both were shocked to have fallen victim to such a crime. Mrs Johnson has no idea how the criminals managed to obtain her details.

She said: “I have always been careful - to the point that when I put my PIN number in, I put my hand over the keypad. ”

Warwickshire Police spokesman Kate Turner confirmed the force was aware of the fraud.

She said: “An investigation is currently taking place in Warwickshire into the fraudulent use of credit cards. A member of staff at a garage in the Hatton area is assisting police in a bid to identify suspects.”

She added that a special police unit in London investigated instances of cloning and fraud, and that victims of credit card crimes should first contact their bank or credit card company.

In November 2007, customers in Kenilworth reported cloned cards had been used for cash withdrawals in Malaysia after using the Shell garage in Warwick Road. Shell denied links with fraud at its Clarendon Avenue service station in Leamington after a customer there also had money withdrawn in Malaysia.

Shell spokesman Sarah Smallhorn Guppy said the company could not comment as this was an ongoing investigation. She added: "Shell is committed to stamping out this type of crime, and we continue to work very closely with the authorities and the banking industry.

“Any customers who believe they have been affected should contact their card issuer immediately," added Ms Smallhorn Guppy.