Frost damage probably, if it happened before the most recent hot weather. Drought is the other possible cause, but I wouldn't have thought that would be an issue, unless its in a pot and you forgot to water it.

Thanks for your reply. I planted the tree in the ground and it now stands about 6ft high. I have a much older apple tree in the garden but it has not been affected.
This has only happened this week.

Hmm, well any chance you can post a photograph?

I'll take a picture tomorrow and post it on here. I'ts a bit late tonight. Will that be ok?

Oh yes, I'm logging off shortly anyway.

Hi Bamboo. I have put a picture on here of what the leaves look like on my tree.Does this give you any ideas about what has caused this to happen.

Checked the photo - its a bit blurry so I can't see detail, so can't tell whether its got mildew or anything, but I do note there is new growth at the tips, so whatever it is, the tree is growing on regardless.

Thank you for responding. Looks like I have to wait and see what happens next.