You don't give much to go on but I would say it's over for your Hebe if it has taken up the poison through the roots or leaves, it's everywhere. The whole plant is infected.

well you have nothing to loose. take any 3-6inch sections that don't appear to be affected and remove all the lower leaves leaving 2-4 upper leaves. push them into a gritty compost, water well and place in a warm well lit place. you may be lucky and get some to root.

can you upload a photo of your affected hebe?

welcome to GoY too :o)

thank you both. I'll try and get a photo uploaded.

Can you describe the symptoms? How long has the plant been in place?
Several folk much wiser than me have pointed out that with problems like this it's generally soil, soil, soil!! Have a gentle dig around the roots. Are they overly constricted? Are there pests? Is it too wet?
As a last resort, lift it, wash all the soil off the roots &, depending on size, put it in a container with fresh, free-draining compost.
Generally with over-spray of systemic herbicides you see strange growth effects called fasciation

Fasciation can also be caused by physical damage at a growth point [aphid damage etc] Darren.

Sorry Seaburn that was the best advice I could think of.
Is it the physical damage or an insect related virus that causes the problem?

can be either apparently Darren.