Well i've got the bonnet open, and as suspected it's the plastic connector that's caused the problem, or more accurately, the metal ring that is clamped over the plastic sheath/outer cable has shifted (because the underbonnet temps are pretty brutal out here) allowing the outer sheath to travel rather than the inner cable.
For info: Using a hacksaw blade, you can ease the kidney grills out of the bonnet, this allows you to release the left hand bonnet release by yanking on the cable that runs under the front cross member. You can't get to the right hand one through here though.....
To release the right hand one, pull off the lens cover from the RH headlamp. EEEeek I know!!!!! , but mine didn't break and all i'll have to do is silicon it back on after the plastic clips broke. This reveals a space behind the indicator that allows you to ferret around to locate the release cable that runs over the headlamp and up the inner wing. Good tug on that and hey presto
I've now figured a way to clamp the cable into position to stop it moving about, a loop of strip metal, folded around the stripped outer cable and screwed through onto the inner wing seems to have sorted it.
Shame it's such a crappy design to start with!