Not easy (even with the specimen, probably). Perhaps a species of Dendryphiella. I can’t track down anything from the host that it might be, but it may well be saprotrophic and therefore not host-specific. Sorry not to be of more help…
Thanks for looking, Paul. I wasn’t too optomistic as I know how difficult they can be. As we were in the teeth of another gale I grabbed something from the greenhouse.