Bonnet stuck!
Same thing happened to mine. Remedy involved a long screwdriver forced between the bumper and the grill acting as a lever on the lock mechanism. It caused a few scratches on the edge of the bumper - not really noticeable unless you know that they are there - and someone lifting the bumper while the other guy did some "fishing" with the screwdriver. It wasn't an easy job and the guys earned their twenty quid, but having watched how they did it, if I had to do it myself I could have done it with a bit of assistance from someone to lift the bonnet. It would have involved much more swearing though!
What happens is that the mechanism seizes and the steel where the cable connects bends instead of releasing the latch. Because of this it takes a lot of trial and error to get the screwdriver to lever the right bit.
From now on mine gets regular oiling!
Hope this helps.
Good luck.
David