Thanks for your reply :)

It’s interesting that all the imagery aligned with each other, but the Cadastral Parcels (or a high-accuracy GPS trace) are the source of ground truth for the UK, as they’re higher precision (and hence easier to align to) than aerial imagery.

It might be that Horton has a systematic parallax error in aerial imagery due to its altitude or the fact it’s in a fairly narrow valley.

I’ve reverted it as https://www.openstreetmap.org/changeset/168352371