I believe (without checking) that this is the last Ealing comedy which I hadn't seen.
It starts off slowly and rather unpromisingly. Our setting is the Outer Hebrides late in WWII; the inhabitants of the small isolated island of Todday [check] have run out of whiskey - general despondency and gloom ensue, since it seems almost everyone is seriously - but comically! - alcoholic. (Hey, they live in the Outer Hebrides. Give them a break!)
Luckily for the islanders, fate intervenes: a ship wrecks nearby, with a stranded cargo of 50,000 cases of whiskey. (Based on a real incident during the war.) They all rush out to salvage as much as their boats can carry - well, they do as soon as the Sabbath ends, just after midnight. They are Presbyterians, after all.
For the antagonist we have the martinet Captain of the Home Guard on the island. He is determined, just for the sake of the forms of things, to prevent any looting. When that fails, he's on the case to retrieve the stolen cases (as it were), and he can't comprehend why no one on the island is willing to back him up. Never mind, he'll bring in the excise men from the mainland!
In the last third the movie heats up and we have some lively chase scenes, and the Captain's concluding comeuppance is apt. We end with an ostensibly moralistic anti-alcohol voiceover, which IMdb tells me was added for the Yank release. I wonder if that's true: it seems pretty clearly a pisstake to me, and as such it works well.
Marginal thumbs up, despite the slow beginning. Good quirky islander characterizations pushed it over the top.