Apparently there are dozens of fungi species with first recorded presence in Britain being of them growing on wood chip mulch. Redlead roundheads are one such mushroom. They were first noticed sometime back in the 1950s or 1960s, and have now spread pretty much everywhere. They’re spreading across western Europe and north America too.
Originally from Australia, and now beginning to be seen in woodland leaf litter: but the only ones I’ve ever seen are on wood chip. Quite common from late summer to late autumn in parks – these were in Bantock Park