A convenience store manager has warned fellow shopkeepers to be on their guard after losing �400 in a scam involving pre-paid credit cards.

Nigel Dowdney, who runs the Stalham Shopper on High Street in Stalham, said his store was targeted by two men at about 9am this morning (Friday).

They handed over a pre-paid card, which can be topped-up with cash at certain shop counters and used as an alternative to debit or credit cards for online transactions.

The cashier uploaded the requested sum onto the card, but before she could take the cash, the men ran out of the shop. Three minutes later, the money had been withdrawn from a cashpoint using a duplicate card.

Mr Dowdney said: 'They were very slick and they have conned the shop assistant. When she turned around to take the money, they said they didn't have enough and ran out of the shop.

'We are �400 lighter and they are �400 richer, and there is little we can do about it. There are a lot of other shops where that money could be the difference between making a profit and not making a profit. We think two or three people are targeting similar shops during busy periods.'

Mr Dowdney advised all shop staff to ensure cash was in the till before the sum was loaded onto the card.

A Norfolk police spokesman said the incident was being investigated.