Interesting! My neighbourhood in London (NW6 - not particularly upmarket) seemed to accept them fine... as well as most places in Central London.
Interesting indeed! My area has lots of tourists doing short stays, so I would've assumed that shops would be MORE open to accept all sorts of cash, but nope. Most places have notices that say they don't accept the £50 notes due to fear of counterfeits.
Shops can refuse to accept them but if you are using them to settle a debt; pay restaurant bill / taxi ride then they cannot legally be refused.
Cue debate about if stamps must be accepted!
Yes they can. It means they can't sure you for not paying though.