My brother happened to be passing through Oxford and dropped in. Great to see him and, as usual, he answered all my trivial electrical questions. I think that if I didn't know he could enlighten me, they would all pass straight through my mind unnoticed, but there's something much more interesting about a puzzle that might have an answer so I hold on to them until we meet. The most surprising information I gleaned, having told him about the toaster tripping the consumer unit over the weekend and me discovering that some of the circuits were wrongly labelled*, was that mislabelling is not uncommon. I'd have thought that was unsafe.
He also helped me on the first step towards combatting some of the summer overheating of this house due to solar gain.

After he left I offered to donate my old slates to the roofers working down the road (no - they have a yardful), handed 40 of them to someone who'll use them in her allotment, went to the dump with some half-pavers that no-one seems to want, and cycled to town to replenish the post-weekend fridge.

*Yes, over the weekend I did check every circuit and relabel them, with the help of Firstborn running round the house switching things on and off.