DETECTIVES investigating an early-morning armed raid at a service station believe a robber may have hidden on the premises the night before he struck.Police said there was a "strong suspicion" that the gunman had already been in the Safeway garage shop in Witham when it was opened yesterday morning at 6am.

DETECTIVES investigating an early-morning armed raid at a service station believe a robber may have hidden on the premises the night before he struck.

Police said there was a "strong suspicion" that the gunman had already been in the Safeway garage shop in Witham when it was opened yesterday morning at 6am.

The robber, who was wearing a balaclava, held a gun to a male worker's head while ordering his woman colleague to hand over cash from the till.

The assailant left with an unspecified amount of money.

Armed police and a dog unit searched nearby sections of the A12 and local car parks in their attempt to trace the man.

But yesterday they appealed for rail commuters to report anything suspicious they had seen either in the aftermath of the raid or on the previous night.

Detective constable Matt Bradford said: "It appears that this man had been in the shop for most of the early part of the morning or even maybe the latter end of Monday night.

"I'm looking for help from people who were walking along Albert Road or motorists who were dropping off loved ones at the railway station to contact me if they saw a man fitting the description of the armed attacker.

"Equally, I will be looking to speak with any residents who live nearby and who saw a man loitering in the area late on Monday night and who fits the description provided."

Police will be examining CCTV footage of the incident in an attempt to identify the robber, who is described as white, about six feet tall, and was wearing a black leather jacket and green coloured trousers.

Yesterday a spokesman for Morrisons, the owner of Safeway, said: "At approximately 6am this morning a robbery did take place at the petrol station adjoining the Witham store, in which cash was taken from the tills.

"There were no customers in the petrol station at the time and no members of staff were hurt in the incident.

"The police are investigating the incident at this moment in time and if anyone has any information they should contact the local police."

The robbery is being investigated by detectives based at Witham who can be contacted on 01376 501212.