Officers are calling on hoteliers to come forward with information if they saw a group of two or three men, maybe with Liverpool accents, around the time of the robbery on or around October 4-5.
A vehicle was driven into a glass door before two men wearing balaclavas entered the building and snatched the cash being loaded into a cash machine.
A green Nissan Navara double cab pick-up truck that detectives believe was used in the robbery was found abandoned in Carters Orchard in Quedgeley a couple of days later on Sunday October 7.
The vehicle was reported stolen from the Merseyside area.
A second vehicle, believed to be a white transit type van, may have been used by the suspects in their getaway.
Anyone with information should ring 101, quoting incident 120 of October 5.
Alternatively information can also be given anonymously on 0800 555 111, or via www.crimestoppers-uk.org. In some cases Crimestoppers offer rewards of up to £1000 where information leads to a conviction.