I would agree with you, Globetrotter --- it looks very much like Clematis vitalba (travellerss joy, old man's beard). The leaves look like Clematis leaves, as does the fact that is was growing over a tree. It's definitely not Crataegus (no offence Bivibave - you didn't have the info about it just hanging off the tree when you made your post). Was it growing in a chalky soil, Globetrotter? Clematis is a calcicole and is almost always found on calcareous or alluvial soil --- most common in the South of England (although I have seen it on the Great Orme - that limestone outcrop in North Wales) - you won't find it on acidic soils. Also, were there any remnants of last years "beards" -- they would absolutely identify it as Clematis. If you go back to the plant around July time, it will be flowering and there a positive identification would be possible.