Cap convex, then flattened, smooth, often slimy, orange yellow to orange brown, and can be up to 10 cm across though often less. Stem yellow orange above, dark brown and velvety below.

Photograph from top down, in side view and from underneath to show gills and full length of stipe.  Note habitat and substrate.

In clusters on decaying wood of deciduous trees.

Found from autumn until winter and unlike most other toadstools it can withstand hard frosts. 

Fairly frequent and widespread in Britain

Fairly common in Leicestershire and Rutland.

https://www.first-nature.com/fungi/flammulina-velutipes.php