I didn't have my camera with me, and grabbed this photo whilst cooking supper
(that's a sliced spring onion in the background)
Following additional microscope work this morning, I am pretty confident that this is O. pumilum sensu stricto rather than O. pallens or O. schimperi. The only old capsules are rather decrepit, but one has an exostome remaining and its split teeth combine with broadly exposed stomata, and the capsule tapering at the base to suggest it isn't O. schimperi, whilst the leaves are relatively ovoid rather than broad-based and tapering, and that indicates O. pumilum rather than O. pallens. The relatively immersed capsules are also more characteristic of O. pumilum not O. pallens (compare it with the Flintshire O. pallens from last year.
The short, hairless, orange-tipped calyptra and tapering capsule base
Split exostome teeth and relatively exposed cryptopore stomata
Ovate leaves (not broad based and long-tapering), and remarkably blunt perichaetial leaves
It is pretty amazing that this third, rarest British member of this species complex has joined O. pallens (Dingestow) and O. schimperi (Abergavenny) on the VC35 list, and is surely evidence that these species are widespread across the country but are only occasionally being spotted.
The site - consummate mundanity!