To eat or not to eat?

A quick foray into the garden produced a lot of potential blips this evening. Most of them contained water that had fallen. (See here for further occurrences.) It had fallen in a very nice way and had made lots of plants appear very bejewelled.

Iris foliage, fuchsia flowers and foliage, crocosmia flowers and foliage. I'm guessing that you get the picture?

But under one of our elm trees we have a huge clump of these. Lots of them and they are big! They are attracting lots of tiny flies, which I assume like the smell of them, consequently eat them and find them quite tasty. Maybe if I'd looked really, really closely, I would've found lots of tiny flies had croaked in the grass after eating my oh, so attractive mushroomy things.

I will give them a miss I think, now that so many flies have dined out on them.

If anyone can tell me what they are and how deadly they are on a scale of 1 - 10, well, I would be very grateful!