I don't seem to be able to sort (ie identify) out wild mushrooms very well. I have even had to check that the usual field mushrooms (you all know - like in the shops) are OK with someone who knows. For me it's berries and things. I do get mushrooms in thelawngrass in the spring which I have been told are edible (is it St George's day mushrooms?) but I don't risk those either.
St George's Mushrooms are one of the easier ones to identify, and are very good to eat - one of the best - but definitely don't let anyone ID them casually for you unless you are very confident they know what they are talking about. Get Roger Philips' mushroom book, and identify them step-by-step. The spring appearance sets the St George's apart from any dangerous lookalikes, but anyone picking all-white mushrooms from grassland should also familiarise themselves with the very poisonous Clitocybe dealbata and Clitocybe rivulosa (although unlike the St George's these usually grow in rings). It's usually also advised to get to know Inocybe erubescens, which doesn't look anything like the St George's but is a poisonous spring mushroom that likes similar habitats.