Anti-White propaganda. This is a thinly veiled revisionist attempt to portray WWII-era Britons as evil villains and the tiny population of non-native blacks living in London at the time as saints. The film's raison d'être is to morally hector, harangue and harass you as a White person and it's time this sort of stuff was expunged from our culture.
AVOID AT ALL COSTS!