After posting I found this which complicates matters
Can I allow guests to smoke in a designated ‘smoking lounge’?
NO: No guest or member of staff is allowed to smoke in any public area of the property, even if all the
guests and staff are smokers.
Can guests smoke in their own private bedroom/accommodation?
YES: But only in certain bedrooms which have been designated as ‘smoking allowed rooms’. These are
for the use of the guest for the duration of their stay. These rooms must be designated in writing as
“smoking allowed” guest bedrooms and a register containing the identity of these rooms must be kept by
the management, and must be available for inspection by enforcement officers at any time. Staff will not be
permitted to smoke in these rooms.
Can any bedroom be designated as a smoking allowed room?
NO: There are certain requirements for smoking allowed rooms. Doors that lead to public smoke-free
areas of the property must have a mechanical closure device fitted, and any ventilation system must not
ventilate into any other smoke-free part of the premises [except another designated smoking allowed
bedroom]. A guest room designated must be clearly marked as a room where smoking is permitted.
So the smokers bar area will have to be in the same space as the dorm so that the whole area will constitute a bedroom.
http://www.breckland.gov.uk/guidance_for_hotels.pdf