I think it's a bit like dress codes. Some pubs don't allow vaping because they're trying to project a certain image. Up to them but stupid and annoying. If you find a pub that allows vaping, it's good to let them know how much you appreciate it, tell your friends, give them a shout out on Twitter or whatever.
I don't usually ask first. I just vape discreetly and am always prepared to say 'sorry I didn't realise' and put it away if there's a complaint. There is a huge difference between in a corner and having a cloud competition across the pool table
I've done both
Vaping works best as a little-and-often thing. It's not like having a fag where you hoover it for 5 minutes every hour or two, so going outside can be much less convenient. It's very tough on new vapers as well, being sent to stand with smokers, especially in a place where they are probably drinking alcohol. I can't think of a better way to sabotage someone's quit attempt.
The Welsh Assembly are currently debating a ban on vaping in all indoor public places (including vape shops FFS!) There's a petition here that anybody can sign and if you live in Wales, there's guidance on writing to your AM here.
Baconyum spreading misinformation about vaping causes actual harm, please stop it. Read this statement from Public Health England (and signed by a further 12 PH orgs):
We all agree that e-cigarettes are significantly less harmful than smoking. One in 2 lifelong smokers dies from their addiction. All of the evidence suggests that the health risks posed by e-cigarettes are relatively small by comparison but we must continue to study the long term effects.
And yet, millions of smokers have the impression that e-cigarettes are at least as harmful as tobacco and we have a responsibility to provide clear information on the facts as we know them to be. It is our duty to provide reassurance for the 1.1 million e-cigarette users who have completely stopped smoking to prevent their relapse. ...
If you're still not convinced, read the full PHE evidence update: An expert review of the latest evidence concludes that e-cigarettes are around 95% safer than smoked tobacco and they can help smokers to quit. Then forward it to your 'friends in the medical professions' because they really should know better.