I don't recognise it as a British native but it may be. cant put a name to it either.

Thanks. The quest goes on! Suspect it may be an escapee but no idea what.

I looked for something similar and the nearest I found was Bird Cherry or Prunus padus. Pretty whatever it is.

I thought bird cherry when I started reading the question but then I looked at the photo and thought nope not that as the leaves don't look right for the bird cherry. The leaves are usually serrated and this doesn't look to be. Are the flowers scented [almond apparently].

The leaves look a bit like Cornus. Could it be a variety of that?

Try Styrax hemsleyana. It seems to fit the description of this shrub/ small tree which grows up to 20ft. Flowers in white racemes, often pendulous up to 6ins long. Origin China.

Thanks so much for all the helpful suggestions. We're going with Bird Cherry at present, but have to go back and have a closer look at the leaves. We didn't notice any fragrance from the flowers but, again, need to look -and sniff - more closely. Styrax hemsleyana is tempting, but the leaves definitely don't look like those in online photos of the tree. Also, the flower racemes look less 'droopy'. However, we're not rejecting that idea yet.