dodgy said:No idea, possibly not legally obligated, but it certainly seems to be the norm.
Just googled around and found:
It is important to highlight the fact that employers are under no legal obligation to provide facilities for smokers. This is left to the discretion of individual businesses. Note however that, in many cases, whatever the good intentions of the employers/occupiers of premises, it will be at the discretion of the landlord’s of business premises whether to give permission for the erection of shelters.
I am guessing that the boss is probably a smoker