Hi Jez.Thanks for the suggestion.I'm currently trying Growing Success cat repellent powder.It smells garlicy and seems to be doing the trick but only when freshly applied(it says 1 application lasts 2-3 weeks),so if I keep my eye on things its not as bad.At least at the minute when they dig their little holes they are doing it between the plants and just scattering them with soil rather than digging them upm like they were when they were first planted.
The plants are all growing nicely by the way and one of the bugle has flowered so I'm well pleased. Thanks for the help and I'll keep you posted.