The yellow boxes have been tested at Bristol and Manchester

Yellow boxes will be painted around cash machines to try and keep customer PIN numbers secret.

One customer at a time will enter the marked area under the self-policing system, similar to road box junctions.

The move follows fresh warnings are issued over a sophisticated electronic scam that has seen criminals target cash machines across south Wales.

Offenders often rely on being close to people using cash points to be able to carry out their crime Project officer Daniel Jones

Cloning devices have been found attached to cash machines to copy cards at banks from Llanelli to Cardiff.

The recent discovery of cloning devices in Cardiff, where thousands of pounds have been stolen from accounts, has taken police by surprise.

Officers first alerted the public at the start of the month believing thieves were targeting machines in the build-up to Wales rugby games.

The latest device, the third recovered in Cardiff, was found last Friday and had been used at two cash dispensers, one in Queen Street and the other in Rumney.

South Wales Police have welcomed the introduction of the yellow boxes saying that unless thieves are able to get hold of personal identification numbers (PIN) most scams fail.

Superintendent Tim Jones of South Wales Police said: "We need to be open to any promising ideas."

Pin number

The Safer Swansea Partnership, which is behind the pilot, said one bank chain had agreed to take part and others had expressed interest in the pilot which is expected to start soon.

Project officer Daniel Jones said: "Offenders often rely on being close to people using cash machines to be able to carry out their crime.

"This may be by trying to note a pin number to enable them to steal and use the card or even to snatch the cash the victim has just withdrawn.

"By keeping others at a distance of just a metre, the opportunity for this type of crime is drastically reduced.