What type of flat is it , ( converted house , small purpose built building containing 2-6 flats , tower block etc ) , there are many different type of ‘flats’ …. some larger type MDU’s can’t be supplied with service until Openreach first obtain permission from the freeholder , managing agent, building owner etc as the building is ‘block wired’ before any orders can be taken , so this pre-fit type work would be known about by the building ‘owners’ ….in some smaller MDU , like a converted house fir example , there isn’t necessarily any work done in advance so any permission necessary should be obtained by the tenant or leaseholder if the flat is owner occupied….
TBH it’s not likely that you will be able to get what your landlord wants , but the pretty obvious thing for the landlord to do is inspect what’s been done , rather than wanting documentation after the effect.
