Supermarkets haven't completely jumped on contactless yet. Around my way, my local Tesco's and Co-op don't support it. Neither do the smaller cornershops, garages, etc. Highstreet stores are more likely to have it. The only shop to have it around my way is a Mcdonalds and a Co-op Pharmacy, not even the Co-op supermarket has it!
I do love the tech though. I think the £20 limit is okay, it just speeds up smaller purchases.
My local Co-op has had it ages, Morrisons have just updated all of their 24 checkouts to contactless, even my dentist has a contactless terminal. The local Tesco, despite being a new build, only open a few months, doesn't, which to me would seem to indicate a policy decision, rather than 'haven't got around to updating it yet'. Confusingly, they have adverts for the tesco bank card posted at the tills, which have a prominent contactless icon on them, which made me think it meant the till accepted contactless.