Could the hedge actually be Box.
Box is affected by a pest called Psylla buxi which leaves white deposits all over it.
I treated a container specimen some years ago with an insecticide the name of which I'm afraid I can't remember, but it did the trick. Sorry I can't be more help, but there must still be a suitable treatment out there.
Thank you for the reply - I think you are right about it being box and not privet so I will check out Psylla buxi and its treatment. Thanks again.