I have a 4-storey building which originally had 2 passenger lifts.  One lift has been removed and the openings to each floor have been sealed to provide horizontal compartmentation to the lobbies on each floor. My question is, would it be expected that vertical compartmentation should now be installed in the redundant shaft or does it suffice to have a smoke detector at the top of the shaft?  My own feeling is that if there are any live electrical services within the shaft that it should be vertically compartmented?

Were the two lifts in a single shaft?

If you look in Building Regulations it's perfectly acceptable to have a protected shaft and not go to the hassle and expense of stopping at each floor as long as the lift shafts have been correctly sealed.

The work should have been notified to Building Control so if they are happy with only horizontal sealing then that should be fine (they won't be reliably certifying that the actual sealing work is done properly though so I'd check the method of sealing and any bits missed)