Help identifying this pocket watch

Your picture of the movement is very poor. It appears as though the serial number is 2713536. If that is correct, then the information on the pocketwatchdatabase.com is:

https://pocketwatchdatabase.com/search/result/waltham/2713536

Your case is English, possibly sterling silver, but could also be coin silver. The 14-size, 3/4 plate movement was made by Waltham, in Waltham, Mass., exported to England, and fitted to an English case. The A.B trade mark is apparently for the firm of Alfred Bedford who was located in the Waltham Buildings, Holborn Circle, London. I believe Bedford was the agent for Waltham in England. This information is from Phillip Priestley’s book Watch Case Makers of England. The lion passant is the English standard mark for silver and gold (22 karat) cases, and the M might be the date letter for 1867-1868. Strangely, the hallmark for London is missing, but the case was likely assayed there. Equally strangely is the fact that the case appears to have been made 20 years before the movement. Perhaps one of our members from England might chime in if I am not totally correct with this information.

Aaron Lufkin Dennison (American) was a principal in the founding of the company that became the Waltham Watch Co., in the early years when Waltham relied on British firms for components that went into American-made Waltham watches. Dennison was the point man in Britain for dials and other movement components that Waltham was not set up to produce. Dennison had emigrated to England, and likely died there. We see lots of U S-made watches in English cases. There were lower tariffs on watch movements shipped there to be fitted in English cases. In about 1875 or so, Dennison founded his own watch case company in England. The trade mark in his cases is A. L. D. It is very common to see Waltham movements in Dennison cases in Britain.

I was watching a You Tube video this morning. I took a screen shot of a picture showing a building in London, England, circa1910. It clearly shows what appears to be the store front for a major Waltham Watch dealer. Pure coincidence?