Very likely just a mature specimen of some cultivar of H. macrophylla ('macrophylla' translates to "big leaves"). The Swiss 'Teller' series all tend to have very large blossoms - "teller" means "plate" or "serving dish" in English - but these are mostly lacecaps. Mophead types that produce very large blossoms (and individual petals) include 'Enziandom' and 'Hamburg'.

Hydrangea aspera also can grow into very large shrubs and the subspecies sargentii is known to produce very large leaves with a soft, almost downy surface. These are also lacecap type flowers of very generous size.

I consulted with some of my coworkers on this one; our thoughts on possibilities for cultivars with particularly big blooms were H.m. 'Mouselline' and H.m. 'Otaska' (or 'Otaksa'- no good consensus on spelling), both of which get very large. I've also seen 'Merritt's Supreme' specimens with oversized blooms, but in truth, there's no way to know for sure; most mature macrophyllas can produce very large blooms in ideal conditions. If I had to venture a guess, I'd say 'Otaska', based solely on its old age and European origin, but it could easily be Enziandom or Hamburg, as gardengal recommended, or any number of others. I hope these suggestions at least help you find something similar to the French beauty that caught your eye!

PS: If you remember anything else about the shrub (i.e. how light/dark the bloom color was, or overall size and legginess, we could possibly refine the search a little, but it would still be educated guesswork)

wild, 'Otaksa' does produce very large flowers, but its origins are from Japan......how likely it would be found in European gardens is anyone's guess :-) But it sure has been around awhile so certainly possible - a lot of Japanese intros of all sorts of plants hit Europe before they manage to make it to north America.

Photos of the plant in bloom would be ideal, but barring that, I agree that we are just posing possibilities :-)

Come to think of it, 'Otaksa' doesn't sound particularly European. :) I have to admit I don't really know much about the cultivar beyond what a coworker told me when we were pondering this question. Anyway, I hope you've found something that fits the bill, vrba!

Otaksa is often seen in new zealand gardens, so I wouldn't be surprised if it made its way to the uk long ago.