Trying to put in a new network cable in the house and starting to think whomever originally wired this place up was a fan of M.C. Escher.
Victory! Maybe. The new network cable has made it all the way upstairs, via under the house for some reason. I haven't tested it yet but... I'm sure it's fine :-)
@fsphil I think that's just how UK housing is, especially after a couple of "just put the new cables in, don't worry about the old ones" rewires.