We have recently set up access to BFI InView. It contains over 2,000 non-fiction film and television titles from the 20th century to the early 21st. It is easily searchable and clearly organised under six main Themes, each with an introductory essay by an academic historian.
From the BFI website: "Carefully selected from the vast holdings of the BFI National Archive, InView's Collections capture diverse perspectives on events, developments and debates, and are supported by informative and authoritative commentary by BFI curators and other specialists. Explore and download rarely seen government films, written documents, newsreels, TVdocumentaries, discussion programmes, parliamentary recordings and much more in an indispensable resource for any study into the recent history of Britain."
You will need to login to access the resource.