This is one of those things people who pay cashless think (including me, although Im not in the UK) because no one pays attention to how other people pay for things.
I was still caught out at new year, when a Chinese takeaway near Barbican wanted cash for a £4.50 sale.
I'm used to paying for that type of transaction with a card in Denmark.
(I paid partly in Danish coins, since I didn't have enough sterling and the cashier liked the resemblance to old Chinese coins with a hole in the middle.)