Police are warning people to be on the alert for a credit card scam that has even fooled people in the force.

Scammers will call targets claiming to be from Visa or Mastercard and say: "This is (name), and I'm calling from the security and fraud department.

"Your card has been flagged for an unusual purchase pattern and I'm calling to verify. This would be on your Visa card which was issued by (name of bank). Did you purchase an anti-telemarketing device for £497.99 from a marketing company based in London?"

When the cardholder says no, the caller continues with: "We will be issuing a credit to your account. This is a company we have been watching and the charges range from £297 to £497, just under the £500 purchase pattern that flags most cards.

"Before your next statement, the credit will be sent to (gives the address of the cardholder) is that correct?" The victim says yes and the caller then says: "I will be starting a fraud investigation. If you have any questions, you should call the 0800 number listed on the back of your card and ask for security. You will need to refer to this control number." The caller then gives a six-digit number.

He then says: "I need to verify you are in possession of your card." He will then ask the victim for the three-digit security number on the back of the card. This is what he has been after all along.

He will say: "That is correct, I just needed to verify that the card has not been lost or stolen, and that you still have your card. Do you have any other questions?"

Anyone who gets such a call should hang up and call Visa or Mastercard directly themselves to check if their card has been fraudulently used.

DC Greg Brunt, Bristol's financial intelligence officer, said: "Payment fraud is an organised crime that has continued to evolve on a global scale.

"Despite constant innovation in fraud prevention, thieves will always be persistent in finding new avenues to perpetrate their trade.

"I would ask Evening Post readers remain vigilant to these new forms of fraudulent attack and ensure they protect their money by never giving out their card's security number."