My grandparents were publicans 70+ years ago. Even they they made very little on beer. All the profit was spirits and software drinks. Probably food as well now.
You could buy a bottle of Teachers and serve yourself 25ml for 70p. You could buy a bottle of 30-year aged Macallan matured in sherry oak, and serve yourself 25ml for £160.
In a pub, you should be able to get a shot of blended whisky for about £4-6, and mass-market single malts (the kind you also find in supermarkets) for about £5-£10.
If you don't ask for a specific whisky, they should ask you which one you want, and/or say "is name alright?" and give you one of the cheap ones.
https://www.mirror.co.uk/money/personal-finance/finance-expe... shows how little pubs make per pint, very sad.
If anyone's curious about cask beer https://www.youtube.com/watch?v=_ud_eTwY4nc&list=PLyDTS7ZG3z... is a very interesting youtube video series by The Craft Beer Channel.