I agree with Wee Brian
This is my take on the situation:- (and Im ready for the flack that I get back for this)
AFD REQUIRED IN COMMON AREAS IF THE PREMISES ARE:-
1) a HMO
2) Self contained flats not constructed to current building regulations
3) Flats converted for sheltered housing purposes
AFD NOT REQUIRED OR POTENTIALLY UN ENFORCEABLE IN:-
1) Self contained Flats built to current building regulations
2) Block of individual privately owned flats *
3) Block of individual privately owned flats where some of the individual owners then let out their flat (ie mutiple landlords)*
* This is where things get complex, the whole thing kicks itself up the backside, and common sense and quantum physics all break down.
In these instances I have known Fire Officers suggest that AFD should be installed within the common areas of the block because they can't control what goes on within the flat. I understand that logic, but unfortunately attempting to enforce that would be a nightmare if the residents failed to comply. (residents would be seen as the RP)
Multiple landlord scenarios in my opinion could get very messy too.
Furthermore the question of common fire alarm systems is apparently discussed as being potentially a bad idea in Colin Toddddd's guite to BS 5839 Part 6
see
http://www.fire.org.uk/punbb/upload/viewtopic.php?id=2697 for further info - I didn't get much response in terms of peoples opinions on that