Smoking in the film studio/ theatre/ on TV is allowed as long as it is part of an ongoing dramatic situation.
Some Local Councils have taken the non smoking rule a bit far by trying (usually unsucessfully) to force theatre directors to stop any smoking in plays,even when it lends period flavour to the play.
TV Studios/ Film Studios being seperate and enclosed do not usually have such laws enforced.
Your question has largely been answered but I'll just add that (other than in film studios, etc, as above) it's not smoking tobacco which is banned in public enclosed spaces, it's smoking anything which is banned. It's just as illegal to smoke to smoke herbal cigarettes in a bar, restaurant or work place, as it to smoke tobacco.
If the studio is owned by a private company then it is private property. Whoever they designate to smoke can...as long as the appropriate health and safety mesasures have been passed.
socket2008 - I think you'll find it is exactly the same as most offices, clubs, shops etc. around the country. Whether it is "privately owned" whatever that means, is irrellevant. It is a place of employment, and in general is subject to the same laws. So the owner cannot just allow people to smoke as he chooses. Apart from the exceptions posted above.
have you seen the electric cig it unbelievably realistic, my friend bought one as a novelty even the smoke looks real but i said this would cause many arguments in a bar / pub people thinking he could smoke while others could not as its not a cig in the real terms the owner would have no legal right to tell him to put it out(or switch it ff) silly idea really,and as i told him for silly people to buty
deggers is correc t I have seen the new smoking cigs.... you can use them in pubs and bars...I was discussing it in the piub with a man the other night who had one.. they contain nicotine but not tar,, Also I have seen them advertised with a picture of Dot Cotton next to it... So I assumed from that she was smoking them in E.A.....They are perfectly legal in pubs...and apparently they do help to top smoking the real thing.. Not especially cheap tho..