One of two. Stem white in colour.
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
Not sure about A.campestris. It looks right, but I find the white Agarics quite hard to separate. Probably best to ID it as just Agaricus sp.
Also useful to see some photos of the stipe (stem) to see if there is any discolouration to rule out the Yellow Stainer A. xanthodermus, and to look at the ring etc.
OPAL Community Scientist
Yorkshire and Humber
I've now added a picture of the stipe as requested.
Hope this helps.
Lat/Lng: 50.8097, 0.191931
OS grid ref: TQ545034