That is a problem too, the staff don't enforce it. If they seem someone in the queue, they will usually tell them to stop smoking.
It's the same situation when it comes to queue jumping, off topic I know. But in my experience staff don't act at all. I once stood up to a couple of girls in the queue for rumba rapids who were just pushing past everyone, and I stopped them and said they're not queue jumping, it's not allowed, and I tried my best to stop them but they laughed and went through anyway, grrr! As it was our turn to get on a boat, their boat was just leaving, and I told a member of staff that they had queue jumped. When we arrived back at the station, I saw them again and the staff member, and he said nothing at all.
I have successfully stopped people though, and rather than them going forward to their friends, I've had them make their friends go backwards, success!
I've also seen one member of thorpe park staff stop a queue jumper once. A man queue jumped his kids on flying fish right at the front of the queue, right infront of the staff. Th member of staff told the man he wasn't allowed to do that and to go to the back of the queue but he just got angry and security ended up coming to sort it out. In the meantime he held up the whole queue for being such an ignorant *******. But, in the end they ended up riding at the front of the train on the next go. Totally ridiculous, but well done to one member of staff for standing his ground!
There need to be more people like me and him that DO stand up to people, I can't stand it, watching people push past everyone jsut accepting that they're going infront, nooo, that's WRONG! How infuriating, ggrrr! ran, rant, rant!