I know Bruce, who also runs his own Scotland forum, is usually very good at guessing places in Scotland. I however will have a go for it as well and think, and hope, it's Loch Carron. Actually before answering I should have asked if this is a sea loch or not. In the very likely event that it's not Loch Carron can you answer that question please?
The Maggie is one of Ealing studios lesser known comedies. A wily old skipper of a Western Isles 'Puffer' and his motley crew lead all who come into contact with them a fine old time! Many scenes on Islay!