Hi Pete,
An awkward Clitocybe for starters, so knowing Ken is probably looking over my shoulder

I shall be very careful by saying did you take a sniff ?
This looks a little like
C.fragrans, but they do seem to be on the large side.
Second shot is the Chicken Run fungus - I'm the chicken, and I'm running away from it as I don't have a clue ! I'll kick myself when told.
Your last, I had in mind Melanoleuca until I re-read your script and your mention of a possible Stropharia, so a big rethink on my part, um, um, well there is
S.hornemannii, that has a central umbo, ain't British though as far as I know. Nope, sorry Pete, bring in the experts.
Neil.