I can see an Elder on the right in the photo - could it be part of that? Elders often go reddish in autumn.

Sorry Landgirl100 - it's part of a bark fencing that I had put up for privacy. Last year about 2 metres of my hedge died and some kind members of GoY suggested I dig up the dead hedge and wait for a year - which I did. But yesterday I discovered this purply-leaf and wondered if the rest of my hedge will follow suit. I had intended to plant some privet hedging next week but if the rest of the hedge is dying, well .............................

Can you peel off a small amount of bark on the trunk of the affected plant? If you see white growth there it looks like honey fungus is killing your hedge. Is there a tree stump nearby, and have you seen any clumps of light brown toadstools?

Yes Steragram - this is what you advised me to do last year and I dug up the infected parts of the hedge (about 2 metres).
After a year the hedge seemed to be OK but yesterday I discovered these purple leaves and I am looking for advice as to whether the hedge is kapout or not!

If it was honey fungus the hedge is probably doomed in
the long run, but the frightening thing is that other shrubs may well be at risk too. You need to confirm that this is the trouble though - did you find the white under the bark or see any toadstools? When you dug up the dead shrubs before did you see any black bootlace-like stringy stuff in the soil?

I can't remember now Steragram! I do remember though that in autumn I did have toadstools which seemed to be growing where the roots of the tree must be. Not sure if I had them this year. I'll delay buying new shrubs and see if the rest of the hedge changes colour.
Thank you very much for your valuable advice.

If you decide to replace the hedge, which will probably be necessary in the long run, you should research shrubs that are not affected by honey fungus or you will have the same problem all over again. Remember that if the fungus is the problem and you wait for it to spread through the whole hedge the fungus will have spread too and may attack other shrubs. Have a read of this:
https://www.rhs.org.uk/advice/profile?PID=180

Thanks you Steragram - will have a read of the RHS article.
I hope I don't have to replace the hedge as it runs up both sides of my garden (20 metres each side!).

Well if only one side seems to be affected you could always have a non matching one. Or even a collection of different shrubs instead - I've been gradually replacing a privet hedge with evergreen shrubs of various shorts and much prefer it.

I have come across this many times over the years, where the privet hedge starts to die back from one end and gradually dies back all the way along, this can be a long process over a number of years, sometimes it can start in the middle of the hedge and go either way, the first sign is the leaves going a sickly yellow colour, on occasions this has been caused by privet thrip but when the hedge dies from one end I have noticed whitish fungal spores around the dug out roots, eg a client has lost half of her privet hedge the affected area has been taken out and young yew saplings have been put in they have done ok nd have not been affected the hedge has been slowly dieing back for eleven years now.

Don't you think it is honey fungus then Julian?

Sorry, JuliEn!

No it's definitely not honey fungus.

That is very good news - so glad you saw the question Julien.

Yes, this is VERY GOOD NEWS. Thanks Julien. I will take your advice and replace the shrubs I took out last year. I have lived in my house for 33 years and this the first time I've had these purple leaves. In the four days since I posted my original question the purple leaves have spread a little more intersprinkled with yellow leaves.