Nice one JP
Found these in similar mulched environment in a park in St Albans last year when foraying with Juliejam (She may still have unposted images)
Mycokey has them thus:
images of "Agaricus" ceres (=S. aurantiaca ss.auct.)
And the BC has this to say:
"Stropharia aurantiaca (Cooke) M. Imai, J. Fac. Agric. Hokkaido Imp. Univ. 43: 267 (1938)
Agaricus squamosus f. aurantiacus Cooke, Handb. Brit. fung. Edn 2 (London): 199 (1887)
Stropharia percevalii var. aurantiaca (Cooke) Sacc., Syll. fung. (Abellini) 5: 1016 (1887)
Stropharia squamosa var. aurantiaca (Cooke) Massee, Brit. Fung.-Fl. (London) 1: 402 (1892)
Habitat: On soil and decayed woodchips or mulch in gardens and parks, also (rarely) in more natural woodland.
Notes: Occasional but widespread and increasingly reported. Probably an alien which is now spreading rapidly, facilitated by the increasing use of woodchip mulch in parks and gardens. We here adopt the generally accepted interpretation of this name, but it is likely that the taxon Cooke illustrated was in fact S. squamosa var. thrausta. There appears to be no appropriate epithet for this species, which may need to be described as new."
REF: Checklist of the British & Irish Basidiomycota