Hard to say without more information and preferably a picture or two - could it have suffered drought? How long have you had it? Have you inspected the leaves, stems, branches, and trunk (particularly at the base of the trunk) for signs of infestation or disease? Has it been pruned at all, and if so, when?

Thanks for your comments, I have updated question and added a couple of photos.

In the second picture, I can see a narrowed area on the trunk, about a foot or less from the ground, with what appears to be a darker band above it, where it swells outwards again. Has that area been damaged in the past, or is there a tree tie or wire at that point that would explain the narrowing? And is the darker band just a trick of the light, or could you describe it as a dark brown or black girdle around the whole trunk? Does anything in that area feel soft if you press on it? Any sign of weeping in that area?

I ask because your tree appears to have a root or trunk problem, from the look of the foliage troubles.

That area is darker than the rest of the trunk,i've been told the tree was originally grafted onto something else,on inspection of that area there is a small dark sticky patch of a gel like substance and I think a cat may have been scratching there.

I suspect that gel like substance is an indicator that the tree has canker or gummosis - symptoms include die back, poor health of the plant generally, and eventually oozing or weeping of jelly like stuff or liquid from the affected area. Unfortunately, the area that's affected is near the base of the tree, and there's really not much you can do about it - had it been in a branch, you could simply have removed the branch, but that's not possible where the infection has occurred. The cause is often a result of injury, which then gets infected with a bacteria or a fungus and affects the whole tree. You can either wait for it to die, or see what happens, or have it removed and the roots taken out.

Thank you for your advice,i think i'll leave it as it is and see what happens.

If it survives till next spring, give it a good feed in April and again end of May to try to boost its energy to fight off the infection. You could use a liquid and water it at the roots, (Miracle Gro, the blue powder one) in which case, you could use it more often, or apply Growmore granules around the base in April and end of May, but that would mean scraping back the stones. Its too late to feed it this year, specially where you are, although if you've got some Miracle Gro, you could give it a shot of that now.

what do you think about applying some garden lime.

I can't see the value in applying lime - the tree appears to have been growing fine till it succumbed to this infection, so I imagine the soil conditions were appropriate already, and changing the ph won't help now. Liming can be useful for fruiting trees, but yours is ornamental anyway

Thanks for all your advice,i'll try the miracle grow,see what happens and feed again next year.