This is a medium sized fungus with a smooth sticky cap.  The colour of the cap is deep blue-green, fading to yellowish, with scattered  fragments of white veil.   The stem is whitish, with woolly white scales below the ring.  The gills are dark without a white edge when mature.  The smell is insignificant. 

Verdigris Roundhead Stropharia aerunginosa has darker gills with a distinct white edge; it is less common than the Blue Roundhead. 

The Peppery Roundhead Stropharia pseudocynaea is occasional in Leicestershire & Rutland; it is also blue-green but has a smell of fresh black-pepper, and a faint ring-zone

The Aniseed Funnelcap Clitocybe odora also has a blue-green cap, but without scales, and smells strongly of aniseed.

gill edge

Photograph from top down, in side view and underneath to show gills and full length of stipe; your photos should clearly show the gill edges.  Note smell, habitat and substrate.

In grass and leaf litter.

Autumn.

Widespread and very common (Kibby, Vol. 3, 2021)

Fairly frequent in Leicestershire and Rutland.

https://www.first-nature.com/fungi/stropharia-caerulea.php