I use cash at the burger van, at the launderette, in the barbers and at car boot sales. I can't think of anywhere else. If I see 'cash only' on the door of a shop I generally go somewhere else, even if I've got plenty of cash on me, because I don't want to give my trade to dinosaurs.
As is mentioned in Dave's link, a pub here in Suffolk claimed to be the first in the UK to go cashless a few months ago but a bar in Granary Square in London was cashless when I went there several years ago. (It was more of a 'restaurant where you can order just drinks if you want', rather than a pub though).
You can't use cash on London buses and if you fly into Charleroi Airport in Belgium without carry a debit or credit card you won't be able to buy any tickets for your onward bus or train travel at all.
Many taxi drivers, and even some Big Issue sellers, now prefer to take plastic.
Cash is, thankfully, all but dead.