Wasn't sure if this would be of interest to anyone, but the BFI have opened up 1000s of films from their archive, making them available for free online. These are short film clips mostly, around 3 minutes in length is probably the average, but they're historic captures of various locations throughout Britain. Here's the link http://player.bfi.org.uk/britain-on-film/ Plymouth has some great films dated as early as 1901! Search around for other locations, its really fascinating stuff!
I have also come across this documentary from 1946 http://player.bfi.org.uk/film/watch-way-we-live-1946/. It is directed by Jill Craigie, who met her future husband Michael Foot while shooting this film. It details the post-war struggles of living in and rebuilding Plymouth.
There's another film of the opening of the speedway track in 1930 and another of some Pram Derby of which 50,000 Plymouthians turned up in the streets to see people race with their prams!