It looks like Buxus Sempervirens, Box shrub. Suffering from either Box Blight or Box tree caterpillar. Check for any caterpillars. In my opinion, if this shrub is based in the south east, I would remove it. It's very difficult to get the plant back into health. Pruning back seldom helps.
Click on the links for advice on what to do with Box Blight and the other link is about the Box Caterpillar. Check the shrubs for any caterpillars.
I have not encountered this issue when I used to have Box shrubs, so cannot really advise from my experience. Let your customer know that any treatment or care will not mean instant good results. In the last few years, it's getting more and more rare to see decent healthy box shrubs. Mostly, the healthy looking ones are the ones in the garden centres.
Posts
https://www.rhs.org.uk/advice/profile?PID=760
https://www.rhs.org.uk/advice/profile?pid=96
I have not encountered this issue when I used to have Box shrubs, so cannot really advise from my experience. Let your customer know that any treatment or care will not mean instant good results. In the last few years, it's getting more and more rare to see decent healthy box shrubs. Mostly, the healthy looking ones are the ones in the garden centres.