It is an indication of the health of British horror that fears about hoodies could inspire three films as different as ‘Eden Lake’, ‘Heartless’ and Johannes Roberts’s ‘F’. Oblique, tense and virtually gore-free, ‘F’ is Roberts’s ‘love letter to John Carpenter’, in particular his urban western ‘Assault on Precinct 13’. So the emphasis is on atmosphere and suspense rather than hardcore horror. Worn down by political correctness and the school’s ‘victim’ culture, burnt-out alcoholic teacher Robert (David Schofield) has kept his rebellious daughter Kate (Eliza Bennett) in detention, just to spend time with her. An invasion of the building by faceless hoodies is followed by the terrorisation and murder of other staff. Grounded by Schofield’s central turn, ‘F’ makes much of its limited resources, locking us into its nocturnal world and throwing away the key.