Associated wth Birch.  The cap is 2 to 4.5 cm, dark grey to grey-brown, and  initially covered in grey-white woolly squamules which are  washed off by rain.  The gills are a pale ochraceous-brown. 

Several other species of Cortinarius have grey/white squamules on the cap; e.g. C flexipes (with a strong smell of Pelargonium or house-plant 'geraniums') and C. gossypinus (associated with Salix). 

habitat

Photograph from top down, in side view, and underneath to show gills; note habitat and substrate; check for smell.

Well wooded areas, favouring Birch.

Autumn.

Widespread and fairly frequent in England and Wales.

Occasional in Leicestershire and Rutland.

https://www.first-nature.com/fungi/cortinarius-hemitrichus.php