These were in the soil under a St John's Wort weed I was removing. They were pale pink, spongy and smelt mushroomy. Removing another SJW a few metres away I found some more, also pink. I also found some yellow-tinged ones under a Cocksfoot grass (Dactylis glomerata) nearby that seemed more rounded in shape. I'll make a separate entry for them in case they're different. I didn't have a sharp enough knife to slice one in half but if that's useful I can plan to do that if I come across any more.