Common in this forest over the last 4-6 weeks. With my limited fungi field skills I don't know what the species is. Looks close to Amanita ochrophylloides. Fruiting body c. 120mm diameter in this case, but many are larger.
Agaricus xanthodermus Yellow Stainer - POISONOUS - often confused with Field Mushroom Agaricus campestris. NOTE yellow stain when stem crushed - but NOT always.
Becoming more widespread. In open grassy area.