I remember the Salop change - someone somewhere trying to be too clever and getting away with it, at least until they got fed up of the sniggers from French people.
As far as Thamsedown is concerned, there is/was a tendency to try to be fair to all parts of each new district, even if (or especially if?) it was dominated by a particular town. Thamesdown was an amalgamation between Swindon MB and Highworth RD.
This policy wasn't at all consistent though. In Cheshire we had Vale Royal and Halton, but also Macclesfield, Crewe and Congleton. I lived in the latter and was surprised that the other towns in the district were happy with this name. They could've called it something like "Dane and Wheelock". (Another possibility might've been "Daven" but confusion with Daventry would've certainly ensued.) Maybe the locals were/are practical types believed it was more important that people could quickly work out where the district was.