You'd be surprised, actually. Trusts really have a stick up their arses about that sort of thing nowadays; they're supposed to be setting an example so they don't look like hypocrites when they insist that everything that's wrong with you can be cured through losing weight, quitting smoking, going teetotal and generally never having any fun ever again. I didn't have to wear a uniform at Barts but at Chelsea & Westminster I did, and it was clearly a Trust uniform. It wasn't an everyday occurrence, but there were several occasions when I got stopped while having a lunch-break smoke outside the hospital and got told off by some random busybody about "setting a bad example". Of course, I was working the Diagnostic Imaging unit at the time. Just glad I never worked for doctors specialising in lung cancer.