Can anyone identify this fungus?

The photos aren't the greatest quality, but a few clutches of this fungus have appeared on our allotment. I'm a pretty diligent spotter of the plain old field mushroom; pink gills, peels, smells like a mushroom and has no real ring round the stem. These aren't field mushrooms; their gills are pure white. So, characteristics (differences from field mushroom as I know it in bold):

1. Smells of ordinary field mushroom.
2. White gills.
3. About 5-10 cm across.
4. The cap can be peeled easily.
5. Very noticeable ring round the stem.
6. I didn't see a basal bulb.
7. Growing on freshly cultivated heavy clay soil - nearest trees are elm saplings 10-15 metres away.
   

I've been looking around online and I think it's probably some sort of edible Agricarus, but I'm not going to take the risk.