Well I heard back from the IWM today and I've now seen a digitised copy of this film. I don't believe it's from 1970 at all. The manufacturing techniques and the whole 'atmosphere' feel much more like the 1940's. And in fact the credits show that the film was made by Douglas Fisher. This website
http://www.radararchive.com/, set up by his son, indicates that he was working at the Telecommunications Research Establishment, whose name is also on the film, during WWII and that he moved to Burroughs Wellcome after the war.
The film doesn't go into any real detail about the resistors themselves. But it does show them being put together, painted, tested and packed. The working techniques and conditions are really rather primitive. The film is silent with captions but, surprisingly perhaps, is in Kodachrome colour.
Cheers,
GJ