Still no takers! hmm. Yes it's definitely a strange one. Here's a couple of photos of what I can only presume are/were its "flowers". However, they are hard and brown and remain throughout the year. Even in the winter when the tree is totally bare of all leaves these hard brown crunchy things remain. Perhaps it is diseased?
Its an Ash - Fraxinus excelsior - but it looks odd because much of the inflorescence is attacked by a gall-mite, Eriophyes fraxinovorus. Although the infestation here is severe you can still see the tree producing some of the typical winged ash-key fruits. It is a fairly widespread and abundant gall. The mites are most active in September-October but as you noted the structures they form persist throughout the year.