The Metropolitan Police Specialist Crime Directorate has issued a warning to the public about the re-emergence of a fraud that has been around for a few years.

The scam, dubbed 'criminal cashback', is aimed at anyone who advertises something for sale, be it over the internet, in the local paper, in the specialist press or in a shop window.

According to the Met, average losses are now running at between £3,000 and £5,000 per victim.

The victim will be contacted by the criminal posing as a buyer and will rely on the fact that their victims don't fully understand the banks' clearing systems for cheques and will therefore believe there is no risk involved.

Whatever the price of the item for sale, the 'buyer' (or their agent/associate) will send a UK cheque or bankers draft for significantly more than the asking price.

The 'buyer' will then enter into an agreement with the vendor that this overpayment will be returned to them via 'money transfer' or sent to a third party or shipping agent once it 'clears' in the vendor's account.

Once a cheque/bankers draft has 'cleared' it will show in a bank account as a credit and the 'overpayment' can be drawn out.

However, the cheque is either forged or stolen and won't actually make it through a bank's clearing system for up to two weeks.

When this happens its value is debited from the victim's account and, unlike many other online crimes, the bank will not be liable for the losses.

Because incidents of this type have been growing rapidly, the Met has worked closely with the British Banking Association and APACS to try and raise public awareness to prevent further offences and disrupt the criminal gangs.

DCI Stuart Dark, from the Met's Economic and Specialist Crime Unit, said: "The advice to anyone who is selling something is not to accept a cheque or bankers draft for any amount over your asking price.

"You should also be suspicious if the buyer appears reluctant to meet up to view an item for sale where this would be the usual procedure.

"If you have already been overpaid for an item, do not transfer any cash from your own account to anyone connected with the deal by money transfer even if their funds appear 'cleared'. Don't be afraid to seek advice or to terminate a sale."

Anyone who thinks they have been a victim of criminal cashback is advised to contact their local police. More details of the scam can be found on the Metropolitan Police website here.