I’ve found this blossom in the grounds of my local village hall. I’ve checked my tree book and I’ve been on-line; but I can’t figure out what it is. Any ideas?

I’ve found this blossom in the grounds of my local village hall. I’ve checked my tree book and I’ve been on-line; but I can’t figure out what it is. Any ideas?
I wonder if it’s in the same family as the white champion?
Trouble with it is that it’s a small tree. It’s got me stumped.