Inside scoop: the pub group who owned that pub (still going, owns four in Cambridge and environs) was cofounded by Steve Early, a Cambridge computer scientist who wrote his own POS software, so it was very much a case of "yeah, that sounds like fun, I'll add it". (Until tax and primary rate risk made it not fun, so it was removed.)

The POS software's on GitHub: https://github.com/sde1000/quicktill

For anyone who takes doing their taxes seriously, this is a nightmare. Every pint ordered involves a capital gain (or loss) for the buyer. At a certain point you're doing enough accounting that you might as well be running the bar yourself (or just paying in cash)!