This tree is in the gardens of Petworth House and looks amazing now (May). Does anyone know what it is?
Looks like it could be the 'handkerchief' tree. Google it and see if any images match what you saw.
It's the Davidia involurata - also known as the Handkerchief Tree or Dove Tree
Thanks so much both of you, that's exactly it. Very beautiful and unusual when it's in flower which I guess isn't that long but still! thank you!