Off-licence owners have been warned by police to be on their guard against two youths who have carried out a series of robberies using a stun gun.

The two males have robbed seven stores across West Sussex during the last month, each time threatening the assistant with the device which can emit an electric shock.

The robbers, who are thought to be in their late teens, have struck at stores when there are no other customers inside, usually between 9pm and 10pm.

In each case, one of the youths has bought a low-value item and the pair have approached the counter.

Then the other has pulled out the stun gun and put it towards the face of the shop assistant.

They have then demanded cash from the till.

So far, the youths have struck at Bognor, East Preston, Barnham, Angmering, Billingshurst, and Middleton-on-Sea.

On two occasions the robbers fled empty-handed but in other cases they escaped with up to £900 in cash.

Detective Inspector Jeff Riley said none of the shopworkers had been physically hurt.

He said: "If they strike again, we are asking people to be passive and to move out of the way."

The first male was white, aged 16 to 20, about 5ft 9in to 6ft tall and of slim to medium build.

His accomplice was also white, aged 17 to 18, 5ft 4in to 5ft 7in and of slim build with fairish hair and an angular face.