Why stage plays need a character that screenplays don't

Alexander Mackendrick didn't just direct The Man in the White Suit: he wrote the first draft of the screenplay.

In his book Lethal Innocence: The Cinema of Alexander Mackendrick, Philip Kemp quotes Mackendrick on the genesis of that screenplay. It began life as an unperformed theatre play by his cousin Roger MacDougall:

"I did something really wicked: I took Roger's hero and gave him a minor role, and pivoted the whole story around a secondary character, the one played in the film by Alec Guinness, to make a new story entirely. And Balcon liked it, and approved it. When I showed it to Roger he got very indignant, and said, 'My God, you might as well have cut the hero out altogether!', and I said, 'Yes, well, I did actually think of doing that.'"

Having got over his initial pique, MacDougall went along with the further disruption of his play, and with the total elimination of his hero. "Something I discovered then," he recalls, "is that there's a character you need in a play, but you don't need in a film, because the camera takes over from him. It's Enobarbus in Antony and Cleopatra, it's Horatio in Hamlet. The camera becomes that character who holds it all together – the viewpoint character, if you like. You don't need a person to do it for you."

Next time I watch an old British film that's too obviously been adapted from a stage play, I shall try to work out which character should have been left out.