Hello, as with most hebe's they do get very large very quickly even if they are trimmed each year, you could try trimming it lightly without going into that old wood and then carefully wire it so you bring it all together and make it compact, sometimes you have to be ruthless and grub them out and start again, certain hebe can be cut hard back and respond however some can take forever its a painfully slow process far better to either pick a new one up or take some cuttings, on my rounds i deal with wayward hebe on a regular basis, another method you could choose is to cut most of the Hebe away, leave a decent large bit, then dig a large hollow nearby, bend it down and fill wth plenty of decent soil it works well and gives the appearence of an established plant.

I had one that looked similar - small white flowers? It was scraggier than yours and I cut it right back to within a few inches of the ground on one side. It did regrow and the next year I cut the other side. It rejuvenated beautifully.

Thanks for your comments and suggestions. I'll try them before I go to the trouble of getting new a new plant.
Regards
Bernard