we will have wait for legal precedence, if ever. 
But we won't my dear Thomas - the Order is quite clear on this, legal precedence is not required.
To answer your question (which I missed first time round) all of the multi-occs I have ever dealt with have had a fire risk assessment for the communal areas completed by the landlord or their managing agents (or atleast they have completed one after my intervention)
Only once have I encountered a multi-occ where one of the tenants have been named specifically in the terms of the lease as responsible for communal areas as they occupied / rented 98 % of the building, with another couple of sole traders renting two very small offices on the ground floor. It began life as simply one occupier renting the entire building.
So why is that so rare? It's common sense - If all the tenants are made collectively responsible for the communal areas (through the terms of their individual leases) then you can soon see the amount of squabbles that would ensue. It would get incredibly complex in large multi occs
Who has the lion's share in terms of decision making? Who is going to take time out of their busy schedule to phone around getting quotes to arrange for the communal heating to be fixed for example ? One occupier might do something that occupiers object to.Its just not practical. Furthermore the landlord won't want people knocking his or her building about without permission, or making repairs that are substandard or not to their liking, so that is why finding a multi occ where tenants are fully responsible for communal areas is extremely rare.
If I'm renting office space in a multi-occ then part of the rent I pay will include service charges for the upkeep of the building. This is normally divided between all tenants proportionately.The landlord will then use that to maintain the building - so say if the heating or the fire alarm packs up I pick up the phone, report it to landlord and he has it repaired.
In the space I rent I exercise a certain level of control over what takes place in there. I can't alter the building without permission as I don't own it.
I can control my stock, my staff, production levels, in the space I rent / occupy - But I don't have any control over Joe Blogg's mob who works down the corridor who share the communal areas of the building with us - So if they start storing boxes in the communal corridor I could go and have a word and ask them to shift them, but they could in turn tell me to "go away".
Instead I would call the landlord and get them to deal with it - because they own the building and can exert full control over the communal area and what goes on in there. Non of the tenants are fully in control of the communal areas - they exert control in their own occupancies not communal areas
Look at the definition of responsible person again, and look at what it states about levels of control. As a tenant you will agree I have no control over the communal areas and therefore by default cannot be the responsible person for them.
If Joe Bloggs blocks the communal means of escape with his boxes of fireworks, and my employees are put at risk then yes as a responsible person (because I am a employer) I would need to take some form of action to protect my staff.
But that action may mean I have to send my workforce home for the day until the means of escape issue has been dealt with because for example Mr Bloggs is most unreasonable and doesn't like being told to shift his boxes by the likes of me so i have to wait for the landlord to intervene!.
