Are you having this long run of dry weather? A good soak under your tree can do no harm, also we have had very hard frost down here, it damaged my vine up to 5ft. and much of the fruit bloom is damaged. Apples, Pears Plums Cherries and currants are full of fruit. We have now had a rainfall of 10ml.

Are the leaves which are changing colour directly behind the withered blossoms on the tree? Are they going brown and remaining on the tree, stems and leaves, directly behind the withered blossom? Or are the leaves changing colour all over the tree, unrelated to the withered blossom? And have you been suffering severe drought up there?

Hi Doctorbob & Bamboo - yes, it has been really dry here for weeks - a nice soaking early on Sunday morning was the first probably since March. I had put the sprinkler on under the tree just a couple of days before - but there is lawn under the tree which is not showing signs of drought. As you suggest Bamboo, the leaves are staying on the tree behind the blossom, turning colour as in autumn and then going brown and dead. The blossom has gone brown too - no petals have dropped on those branches. But the vast majority of the canopy is green, leafy and the baby apples are starting to swell!
Thanks for your help - much appreciated

Sounds like Blossom Wilt to me - get your secateurs out, hopefully sharp, clean ones, and clip off all the brown stems with the withered blossom and leaves as well, take them back to healthy green growth. Do this as soon as possible.

Thanks, Bamboo - I'll cut the branches back this weekend. Have read up a little on Blossom Wilt from your reply, and can only suppose it's the result of heavy dews coupled with warm weather - it certainly wasn't a wet spring!