Weird one this and I only watched it as it wasn't quite an hour long and promised to be an intriguing comedy/murder mystery.
You know who the victim is (a rich uncle) and 99.9999% sure it was his nephew (the Smart Alec) who commits the murder, which has to be accomplished by the next day, when the uncle changes his will, cutting out the nephew.
What ensues is a bit of a farce as the story is "jollied" along by the antics of Kynaston Reeves (Mr. Quelch of Billy Bunter of Greyfriars School 1950s TV Series fame) as the Police Commissioner, Charles Hawtrey as an idiot police detective and Mr Partridge of Hi De Hi fame again (Leslie Dwyer) as a hotel porter - the three of them doing various comedy scenes linked to the plot.
Peter Reynolds (who I'd never seen before, but seems to have had quite a good film career) plays the Smart Alec, who through precise timing appears (and all in front of the Police Commissioner who he deliberately invites into his flat as a witness of his innocence) to murder his uncle who is sunbathing on the balcony of a flat opposite, with a rifle shot. Impossible! So did he kill his uncle or not? Reminded me a tad, of a poor man's Jonathan Creek.
Stupid twist at the end with a bit of evidence that wasn't presented at all in the film - thank Heavens it was only a short film.