Death Line (1972) is an interesting experiment by the Rank Organisation.
It is a very British entry into the domain of Night of the Living Dead & Texas Chainsaw Massacre - with elements of Police Procedural, Gialli, Social Satire (in the manner of H. G. Wells), and Grand Guignol

Donald Pleasence and Norman Rossington play unpleasant pre-Brit-Noir coppers.
Christopher Lee is a hoot in his brief cameo as a René Magritte MI-5 agent.
James Cossins is a posh dead creep.
Marlon Brando was set to play the cannibal, but ducked out when his son caught pneumonia.

David Ladd & Sharon Gurney basically play the same roles that Tony Musante & Suzy Kendall played in The Bird with the Crystal Plumage; only as secondary characters. Gurney’s wardrobe slavishly copies Jane Fonda in Klute.

Donald Pleasence is the standout here. His character is provocatively disagreeable, petty, and small-minded. His patter with Norman Rossington is like a macabre Morecambe & Wise. Rossington, the underling, is paradoxically far more knowledgeable and socially adept than his boss.

Christopher Lee, despite the many accolades he received from the horror community, was never really given proper acclaim as an actor. In Death Line, he creates a surreal aura of menace while smiling constantly and delivering unmistakable threats in an unfailingly polite tone.

Christopher Lee was a cultured and well-traveled man. His background and upbringing somehow simultaneously made him the quintessential Brit and the eternally untrustworthy outsider. His character in Death Line wields the symbols of his class privilege like a cut-throat razor.

Lee performed his cameo in Death Line for scale because he wanted to work with Donald Pleasance. Sadly, they couldn’t share a two-shot because of their vast differences in height. The odd framing and blocking does add a surreal and unnerving edge to an already disquieting scene.

Pleasance, at that stage, had a career mobility that Lee probably admired & envied. While Lee was mainly typecast as a horror villain, Pleasance could transition between potboilers & his work w/ Harold Pinter, Tony Richardson, Laurence Olivier, John Osborne, and Roman Polanski.