Question
I have a Privot hedge at the front of the house which seems to be slowly dying.  Parts are very green and bushy whislt other parts are totally brown and non growing and other sections which are turning brown and again not growing.

Is thjere anything i can do and if not is it easy to re-plant a mature replacement

Answer
Gedglover,
This is a common problem with privets. There are several diseases that can cause this pattern of dieback. I would venture a guess that this is caused by root rot. Check the soil around the hedge. If there is excess water caused by heavy rains or  poor soil, then this is your culprit. Try to amend the soil using compost and sand to improve drainage and increase the organic content in the soil.
I would also recommend that you look at the plants, damage like this can be caused by scale feeding on the bark or aphids feeding on the leaves. In either case, a good coating of horticultural oil will bring them under control.
Fertilize the hedge and see what recovery you can acheive that way.
If you need to replace dead sections, I would recommend going to your local garden center and seeing what size privets they carry. The new plants may be smaller than those that are there, but they will catch up eventually.
Good luck.
Ed Gulliksen