Movies You Haven't Seen But Should: The Ruling Class

Wiki:

The Ruling Class is a 1972 British comedy film, an adaptation of Peter Barnes' satirical stage play which tells the story of a paranoid schizophrenic British nobleman (played by Peter O'Toole) who inherits a peerage. The film costars Alastair Sim, William Mervyn, Coral Browne, Harry Andrews, Carolyn Seymour, James Villiers and Arthur Lowe. It was produced by Jules Buck and directed by Peter Medak. Peter O'Toole described the movie as "a comedy with tragic relief".

Jack Gurney, the 14th Earl of Gurney (O'Toole), at first he thinks he is God and shocks his family and friends with his talk of returning to the world to bring it love and charity, not to mention his penchant for breaking out into song and dance routines and sleeping upright on a cross. When faced with unpalatable facts (such as his identity as the 14th Earl), Jack puts them in his "galvanized pressure cooker" and they disappear. His unscrupulous uncle, Sir Charles (Merwyn), marries him to his own mistress, Grace (Seymour), in hopes of producing an heir and putting his nephew in an institution; the plan fails when Grace actually falls in love with Gurney.

Gurney gains another ally in Sir Charles' wife (Browne), who hates her husband and befriends Gurney just to spite him. She also begins sleeping with Gurney's psychiatrist, Dr. Herder (Michael Bryant), to persuade him to cure Gurney quickly.

Herder attempts to cure him through intensive psychotherapy, but this is to no avail; Gurney so thoroughly believes that he is the "God of Love" that, ironically, he dismisses any suggestion to the contrary as the rambling of lunatics. The night his wife goes into labour with their child, Herder makes one last effort at therapy; he introduces Gurney to McKyle (Nigel Green), a patient who also believes himself to be Christ, or, as the patient puts it, "The Electric Messiah", who subjects an unwitting Gurney to electroshock therapy. The plan is to use the electroshock to (literally) jolt Gurney out of his delusions, showing him that the two men could not both be God, and so he must be operating under hallucinations. The plan works, and, as Grace delivers a healthy baby boy, Gurney returns to his senses and reclaims his true identity, proclaiming "I'm Jack, I'm Jack".

Sir Charles, still intent on stealing the title, sends for a court psychiatrist to evaluate Gurney, confident that his nephew would be sent to an asylum for life. He is once again thwarted, however, when the psychiatrist discovers that Gurney was a fellow Old Etonian, bonds with him, and declares him sane.

Gurney soon relapses into mental illness, however, this time believing himself to be Jack the Ripper ...

[The Ruling Class on the IMDB]

Lady Claire Gurney: How do you know you're God?
Jack Arnold Alexander Tancred Gurney, 14th Earl of Gurney: Simple. When I pray to Him, I find I am talking to myself.

Sir Charles: [exasperated, after meeting Jack] Oh, my God!
Jack Arnold Alexander Tancred Gurney, 14th Earl of Gurney: [ducking back into the room after hearing Charles] Yes?