poor maintenance is a matter solely between the neighbour and his mortgage company

It occurs to me now that there are exceptions to this in the UK: particularly historically or architecturally significant buildings become "listed", which means you need approval for any work done to them -- inside or out -- which might damage their historic or architectural value. Living in a listed building is, apparently, a real pain -- but relatively few private houses are listed. Less strict but more widespread is the idea of a "conservation area", where works must be approved (by the local council) if they affect the appearance of properties as seen from the street. I don't know how that slipped my mind, as I live in such an area! Obviously someone feels that an area containing row after row of two-up-two-down Victorian terraces (the commonest of the common, in every sense, in the 1800s -- as depicted in Coronation Street or the North of England bit of The Meaning Of Life) is quaint enough to deserve "conservation".

Local councils get the power to do this with their powers over town-planning decisions; I still don't reckon they have any power over lack of maintenance, only inappropriate maintenance -- let alone any power to enforce "sociological zoning" of the sort the Georgian Athenians seem to enjoy.

Peter