Four masked men smashed their way into the depot on the afternoon of Saturday July 23, before threatening and assaulting members of staff with metal bars, hammers and machetes.
Terrified staff were forced to hand over cash from the safe, and stand back while items were stolen and loaded into a car which was later recovered. Detective constable Tracey Heneghan, who is leading the investigation, said: "This was a well-planned attack where innocent members of staff were simply trying to do their jobs.
"We are in the process of carrying out a thorough and extensive investigation into this incident, including house-to-house enquiries, and are reviewing local CCTV footage.
"A number of items have also been seized from the depot for forensic examination by scene-of-crime officers."
Anyone who witnessed the incident should call Surrey Police on 0845 125 2222, quoting reference SL/11/5841.