At work we have had to remove several areas of Hebe recently. Hebe's are known for 'keeling' over without much notice - they do not seem to have a great life span in the Hunter Valley, 5 -10yrs. They hate humidity and this past summer has been more humid than previous years. In general I have found that they must have well drained soil as they don't like 'wet feet' prefering being on the dry side. The high humidity provides perfect conditions for fungal wilt. Several of our hedges have been randomly affected by fungal wilt. Removal has been the only option.Living further north than me I'd suggest you save yourself more aggravation and find a different plant to use.
Regards Louise5

Here is a link that might be useful: Hunter Valley Gardens

Thanks Louise5
You have just reminded me that the Hunter Valley Gardens are a good place to look for plants as the climate is very similar to that here in Gloucester. When I last visited- at least a couple of years ago - I remember being a little disappointed at the lack of variety in plants used, However as I now have a little more experience, I realise how relatively few plants will grow in our hot humidity (plus a touch of winter frost) without masses of mollycodling.