The thing is, like it or not, an employer can impose virtually any restrictions they wish, providing they still meet health & safety and employment law.
My employer has banned the use of ecigs on all work premises, including outside areas owned by the organisation AND our own cars while on company business.
Now I disagree with the ban, but I also have to be mindful that I have no legal RIGHT to vape at work, so if I do (or rather, if I get caught
), I might initially get a ticking off, but if I continued, I would work my way through the disciplinary procedure and ultimately get sacked if I didn't desist before it got that far.
It's not the severity of the offence, but a continual refusal to obey any existing rules. If they told me to wear a uniform and I repeatedly failed to do so, I could get sacked for that too - regardless of how minor each individual offence was.
Organisations can set their own disciplinary policies, and as long as these stay within the law and are fairly communicated to staff, staff don't have a leg to stand on if they breach the rules and the disciplinary measures are in line with current policies and procedures