ash burr???

[slackbladder]

Large area of attachment sometimes going right round a branch or most of trunk

[Grandad]

Fascinating, can't find anything that looks like it on the 'net. Never come across anything like that on an ash before. I suppose they are too big to be considered as galls. The tree is covered in them you say? Makes it sound as if it is an insect mediated condition. I hope somebody recognises it for you, I'm dying to know myself!