For a comprehensive description, see http://pyrenomycetes.free.fr/hypoxylon/html/Hypoxylon_petriniae.htm
Common and widespread, not likely to be threatened. Older reports would be under the name HYpoxylon rubiginosum.
On dead, usually rotten wood of Fraxinus excelsior, possibly also on other hardwoods but their identity should be checked.
Found throughout England, also central Scotland, Northern Ireland and ROI.