Detectives say the raiders stole cash from the guard outside a post office in Bulwell, Nottinghamshire.

One of the men pulled the guard out of the premises, took off his helmet and struck him with a gun.

Police said that two other men assisted in grabbing a quantity of cash from the post office security van in the incident on 17 January.

Cars stolen

A Nottinghamshire police spokeswoman said: "Staff and customers were on the premises and saw a man carrying a handgun challenge the guard.

"A struggle took place and the guard was pulled outside and was hit on the head with the gun.

"He was taken to hospital and received stitches to the wound, but is now fully recovered."

The three men drove off in a black Seat Leon but abandoned the car nearby and attempted to steal another car at gunpoint.

The motorist was able to fend them off, but the gang then held up another driver and sped away in a white VW Golf.

Hooded top

Only yards down the road, the thieves pulled a gun on another motorist to steal a blue Vauxhall Astra.

Detectives believe the Seat Leon was stolen at knifepoint in Nottingham on 11 December 2002 and was following the post office security van prior to the robbery.

One suspect is described as a black male, in his late teens or early 20s, of slim build and about 5ft 8in tall.

He wore a hooded top and trainers, similar to Nike shock absorber shoes.