this description of 'ochraceous': a yellowy-orangey-browny colour]. You can sort of see in the photo above that the gills of the smaller (younger?) fruiting bodies are white and the larger ones have turned a darker colour. They just look kind of brown to me though.
Roger Phillips' Mushrooms says that Pale Oyster Pleurotus pulmonarius has a white spore print. So I left this mushroom sitting on a sheet of paper on my desk for the afternoon, to see what would happen.
It could be some kind of large Crepidotus sp. I suppose. The Collins' Complete Guide says Peeling Oysterling Crepidotus mollis grows up to 7 cm across and Flat Oysterling Crepidotus applanatus up to 4 cm - both have a "mid-brown" / "walnut brown" spore print.
I'll have to go back on Monday and see if this fungus has a "peelable cap cuticle", which would make it Peeling Oysterling Crepidotus mollis.
For the record
Location: Woods Mill, private garden
Grid reference: TQ217137