While I'm not condoning nor excusing the behavior how may times a day is a plane landed by a pilot who's got the sweats and shakes from a drinking bout the previous night? I'd venture to say "many"
As far as UK carriers are concerned, I would say virtually never! Where have you been these last 20 years?
I would say these days there's a fair chance of being caught, and if caught, a virtual certainty of a custodial sentence!
There's also a custodial sentence awaiting any captain who knowingly allows any of his/her crew to operate whilst anything less than 100% sober.