The Ladykillers is a 1955 English film. It is one of a series of classic post-war Ealing Studios social comedies that are entirely English.
The plot is simple enough: an especially unpleasant criminal Professor Marcus (Guinness) rents a room in the rundown King's Cross house of a bewilderingly innocent old lady, Mrs. Wilberforce (Johnson), who lives alone with her parrot. From that room the Professor and his gang of curious characters plot a sophisticated train robbery, while convincing Mrs. Wilberforce, by playing records, that they are in fact musicians using the room for rehearsal space. After the successful robbery the gang falls apart in a series of double-crosses executed under the cover of passing trains, through which a targeted Mrs. Wilberforce wanders untouched.
The Alec Guinness role was originally written for Alastair Sim, and in fact Guinness's performance appears to be a very good Alastair Sim impersonation.