Re-my earlier thread on this subject. Just in case anyone else has the same problem, I managed to release the bonnet without causing any damage. I had a close look at the release lever inside the car (head in footwell, feet in the back seat) and found the outer cable was slack, suggesting that the catch was jammed. The catch is quite easily accessible from under the car (both arms up behind the radiator!) and by pulling down hard on the bonnet part of the mechanism it freed it up so the lever then worked.
Much quicker than taking it to the dealers and I learned something into the bargain.
Biggles Remove packaging before e-mailing me