I called it Violet Crust as I didn’t have of the correct name, and I was going to look it up.
It looks inky-blue here, but definitely has or had a beautiful violet colour. Photoed 19.3.15.
Thanks to Peachysteve for the identification.
It’s growing on the underside of a broken hoe handle in my garden, where it was in contact with a plank of wood below it.