6 years on and this problem still arises , except now we could be talking about a 400 quid banger.

Easiest and Quickest method if bonnet opens partly with left turn of key -

Remove lower watershield -8 torx screws all easy. Reach up and pull lock IN , may have to bend 2 clips back.Using sharp wood chisel from front of partly just open bonnet cut heads off the 6 visible PLASTIC screws holding top of the grill in place - use a hammer. Remove grill by pushing back at bottom to unhook and then whole lot forewards.Using wood chisel through the grill space smash all white plastic away from bonnet catch. , remove white cross section bit - pliers . You can now use a screwdriver to open bonnet.When grill is replaced , use extra self tappers if you like ,you will need a longer screwdriver or bar but you will know what is what by now.