FOUR men have been arrested on suspicion of robbery at a Yarm supermarket.

Three masked robbers, one wielding a hammer, threatened security staff delivering cash to a cash machine at Somerfield, in Healaugh Park, Yarm, shortly after 1.30pm on Tuesday.

Another man was waiting as the driver in a blue Mazda RX8 getaway car, and the gang made off with a "substantial sum of cash".

The men from the Manchester area were arrested on Wednesday and are being held in Cleveland, helping police with their enquiries.

Police later found the getaway vehicle abandoned in a cul-de-sac off The Slayde, in Yarm, a short distance from where the robbery took place.

The men were wearing what are described as green jackets, and not high-visibility fluorescent jackets.

Detectives have confirmed they are not linking this incident with five other supermarket raids in the region in the past 18 months.

Det Insp Dave Turnbull, of Cleveland Police, said he was keen to identify the driver of a grey-coloured Ford Focus ST, which was in the area at the time of the robbery.

He said this person may be completely unconnected and is appealing to them to come forward so they can be eliminated from the inquiry.

No-one was hurt in the incident, but staff were left shaken.

Staff in nearby shops said they were unaware of the incident until the police arrived, but they spoke of their relief at not being targeted.

One woman, who asked not to be named, said: "It is a relief, but we don't really take enough money compared to Somerfield."

In the past 18 months, armed gangs have held up security guards at four Tesco stores and a Sainsbury's store.

A female security guard was held at gunpoint and forced to hand over money, believed to amount to five figures, in a raid at Tesco, in Eaglescliffe, on November 16, 2006.

A security guard was also held at gunpoint in Sainsbury's, in Bishopton Road West, Stockton, on February 5 last year.

Another female security guard was threatened with a sledgehammer by two armed men wearing ski masks as she was filling a cash machine in the Tesco Express store in Norton, near Stockton, at about 7.25am on February 14 last year.

In June, three men attacked security guards at the Tesco store in Acomb Wood Drive, York, and escaped with a large amount of money.

Another armed gang held up staff and security guards at Tesco in Parliament Road, Middlesbrough, on July 9.

Anyone with information is asked to contact Det Insp Turnbull on 01642-302226 or Crimestoppers on 0800-555111.