Another suggestion from David S:
In this movie, Peter O'Toole plays the new Earl of Gurney (the last one died wearing his naval uniform and a tutu in a fit of autoerotic asphyxiation). He also happens to think he is Jesus. His idle rich family try to change his disposition so that he won’t embarrass him when he goes to the House of Lords. Then things get weird. Great send up of the toffs with lovely musical numbers.
More at Wikipedia. I enjoyed it. Clearly of its day: the post-"I'm Jack" sequence nods to A Clockwork Orange's "I was cured alright!" and presages The Shining, and concerns around the AC-DC messiah (electro-convulsive therapy) also aired in One Flew Over the Cuckoo's Nest. O'Toole at his fruity best. Mike Leigh's A Sense of History is marginally more respectful.