Possibly a Magnolia? More photos would be helpful.

Certainly looks like a Magnolia bud but a photo of the complete tree is really needed for i.d. purposes.

Thank you but this is all I have as I saw it at an Arboretum and liked the look of the bud.
Thanks again.

Hi, I think it looks like Magnolia grandiflora, it's not completely hardy in the U K, Derek.

Should be OK in Bucks. though?

I would have thought so... They manage to grow up here

I don't have a magnolia in my garden but the bud I photographed was a good sized tree in a local(ish) Arboretum.