case law - you'll be lucky! Proecution is rare enough as it is and usually for more critical things than a few extinguishers in a stair.
Here's how I would look at it-
1. Landlords area PFE is normally risk specfic - plant rooms, car parks, reception (if guard/buliding managers desk with papers, PC, etc)
2. Escape stairs, especially those for fire only, are usually so sparsely decorated as to have no realistic likelihood of anything to use PFE on
3. Some stairway, also used for accomodation (i.e. everyday acess) may be more liberally equiped with ignition & combustible risks (& usually have other common risk areas directly off such as cleaners store cupboards, risers, toilets, etc) and although would not automatically have PFE would be more carefully assessed.
4. Multiple Persons in control or or occupying the same premises shouldn't be doing FRAs in isolation an must coperate and coordinate. As a result with tenants we will always visit them in a landlord FRA to cordinate the FRA, enforce a minimum under the lease and educate (with the new DCLG RRO leaflet as they kindly sent us a free crate of them) them. So they will have suitable PFE that is serviced in their areas (if they want any peace that is)
5. Vacant floors not under lease fall under the landlord and so here we have them either service it or remove it. If vacant under lease the leaseolder is given the same options.
No law or stories to flesh out the above, just experience of hundreds of properties in different brigade areas & not had a problem back yet.
I've seen some daft use of PFE taking the BS too literally e.g. several new builds on their plain concrete/plaster alternative fire escape stair have a fire point of water & CO2 next to the final exit - to be used on what?