Have often found branches and sections of tree without leaves due to disease lower down blocking the transport of nutrients and hormones. This can even be traced to root infections on one side of the tree and whole side of tree affected.
Thanks alan30. this could well be the problem, I will investigate further at the weekend. Any suggestions on how to treat, or is the bush beyond repair?? Thanks again, blobby02uk.
It is difficult to say without seeing the problem. Some things can be treated but generally have found that root problems are difficult if not impossible to correct. If it is an important tree to you then I would get an expert to look at it. If not then a replacement usully gives better long term results provided it is not a fungal infection that can remain in the ground; again expert diagnosis needed.