Consumers are being warned to stay vigilant when after a card cloning device was spotted on a cash machine in south Norfolk.

Police were called to Tesco in Diss at 9.15pm last night to investigate a suspected skimming tool which was attached to the card slot.

A spokesman for Norfolk Constabulary confirmed the presence of the device however there were no lines of inquiries to pursue so referred the matter back to the supermarket giant.

A spokesman at Tesco said: 'We take our customers' security very seriously and regularly inspect our network of ATMs.

'As a precaution we have sent an engineer to inspect this ATM to ensure that the features installed to protect our customers are functioning as normal.

'If customers are concerned about suspicious transactions on their account, we advise them to contact their issuing bank in the first instance.'

Card skimming devices are described by watchdog Action Fraud as 'a small device that fits over the card slot and made to look like a normal part of the cash machine'.

They are designed to copy the information on the magnetic strip of a card when it is inserted and can lead to bank account fraud.

Similarly card trap devices slide into the real slot to prevent your card from coming back out.

After a customer has finished using the machine, presuming their card has been swallowed, fraudsters then remove the trap from the slot along with the card.

According to Action Fraud, the signs to look out for when using a cash machine include a 'wobbly or bulky part that doesn't seem to belong with the machine, such as a cover over the card slot or a loose keypad'.

In order to avoid falling victim to a card skimming scam on cash machines the watchdog advises customers check an ATM every time they use it, always cover the keypad and do not make it obvious which numbers you are pressing.

If you suspect a machine has been tampered with or that you think your card has been affected by one of these machines call your issuer immediately and then report it to Action Fraud online or by calling 0300 123 2040.