Although you could insist on co-operation & coordination so that the two parties at least talk & exchange significant findings, but then there are non fire related issues with it's own law - land law, lease law, etc.
Where ever a route enters another premises, easements and means of escape licenses crop up as an issue - without one you cannot use that route and certainly previous fire legislation could not override this.
Where an easement is not granted in cases we have dealt with this has led in some situations to the stark choices of either spending huge sums on creating a new alternative route on land you have access rights on, or where there is no money or available land to do this change or reduce occupancy or in one extreme case an area became unlettable and rendered obsolete. One shop unit redevelopment was ruined as it's protected exits & stair were in the neighbouring unit and their only stair fully within their unit was a fully open unprotected stair over 4 floors, but they hadn't investigated easments during the refurb and their protected exits had been sealed by the neighbouring shop.
There is no easy answer as adjoining premises exits exist precisely because there is nowhere else to place them within each individual building.
The easy option that most places follow is to ignore the issue and assume with fingers crossed that when the time comes the route will be usable and not have been bricked over on the other side/had a cabinet in front of it/be in darkness and locked up.
I dread London jobs as this is most common here, although a particular street in Liverpool and various places around the country have this issue
