As I said upthread I'm a big fan of this show and see it as often as I can and people singing along on this tour has been a problem.
I think the first issue is that the pre-show announcement is a bit misleading. It asks people to 'refrain from doing their best Meat Loaf impression until after the show'. A lot of people might interpret that as don't sing full throttle but it's ok to sing quietly - which it bloody isn't! Someone droning on in a whisper behind you is very annoying. When it was on at the Dominion there were signs and announcements saying very clearly "Do not join in or sing until the encores' and warning that people who did sing would be removed. No room for misinterpretation.
I think another problem with the tour is that a lot of the FOH staff I'm seeing seem to be very young and inexperienced. I'm assuming they are local students just doing a few shifts. Given that Bat attracts an oldish crowd (I'm 60 and well within the median age range) I think it can be hard for a young usher to approach someone their Granny's age to ask them to stop singing. I think they need more support and training from the theatre management.
I last saw Bat in Edinburgh last week and won't be going again until it reaches Stoke in April. I hope they've got it sorted by then because the singers are spoiling what is normally a great show.