Like Joan Hickson, Katie Johnson is one of those great little old ladies that completely disappears into her character and never needs to do something vulgar to be interesting. She had been acting since 1894, if that tells you anything, and won a BAFTA for this role. Her dainty, pink-clad Mrs. Wilberforce steals the film away from the ladykillers themselves, though they include such icons as Alec Guinness, a very young Peter Sellers, and Herbert Lom. Not that they give poor performances. They're excellent, their sleaziness contrasting perfectly with Mrs. Wilberforce's Victorian sensibilities.
Mrs. Wilberforce lives with her parrots in a lopsided house in London, and is looking to let her upper room. Appears "Professor" Marcus, a creepy, cunning Alec Guinness with enormous false teeth, completely removed from the classy Obi-Wan Kenobi, the only role for which he will (rather unfairly) be remembered. Professor Marcus quickly begins to entertain his friends, a group of "amateur musicians." There's the Major (Cecil Parker), One-Round (Danny Green), Louis (Lom) and Harry (Sellers.) It's not much of a spoiler that they are in fact a group of vicious bank robbers, who have concocted a plan that places the oblivious Mrs. Wilberforce right at the center of their machinations.
Magnificently scripted (another BAFTA win, along with a nomination for Best Film), it's a film that ought to be predictable but is, in fact, full of surprises. It's not a laugh-a-minute, though it does contain a wonderful amount of witty, quietly eccentric dialogue, and this is because it takes the time to develop the story. While after a while it becomes obvious what must happen, the method of achieving it struck me completely by surprise.
Overall, an extremely funny movie, far removed from its 2004 remake. I highly recommend it.