propheller

Can a five storey terraced building divided into five flats have a fire escape over a neighbours roof or into their property? At the moment the house is four storeys and the owner wants to add an extra separate flat in the roof space as a mansard penthouse. Only an extended lift shaft will be able to access this penthouse floor as the stairs stop at the third floor and cannot be extended. They want to connect through to the adjoining neighbours house and to use their protected staircase in case of an emergency. Can this be done? Its a completely different owner and building? The neighbour has agreed (for a fee!). I would say the unobstructed distance is about 10 metres to their staircase. I remember in the 90’s going to a sixth floor flat in London which had an alarmed door in one room and this went through to the neighbours flat, a completely separate terraced property. The door was only to be used in case of fire as an escape route to the neighbours roof. Strange situation. I am wondering what the rules are of using your neighbours property as a means of access in case of emergency.