The owner may still have responsibilitity. let me give you an axample.
a building has multiple occupants, there are no common parts. the building has a fire alarm systems which covers all occupants.
In the terms of their lease, the occupiers are responsible for the general maintenance of there respective areas, but, the Fire alarm remains the responsibility of the 'owner'.
lets say the alarm was in disrepair. the occupiers have shown they have tried to get the 'owner' to repair the alarm but to no avail, in this situation you would not serve an enforcement notice on the occupier, instead the following would be relevant.
(3) Any duty imposed by articles 8 to 22 or by regulations made under article 24 on the responsible person in respect of premises shall also be imposed on every person, other than the responsible person referred to in paragraphs (1) and (2), who has, to any extent, control of those premises so far as the requirements relate to matters within his control.
and on this basis the enforcement notice would be served on the owner.
on the other hand the owner may place responsibility for the alarm within an occupiers lease agreement. and have no responsibility at all.
it really comes down to the terms of the lease