Does the key turn okay in the lock, or is the lock fubar'd?

In the past, I've just used a large drill bit to drill out the lock face. Pulled the tumblers and centre out, then used a long flat screwdriver straight through the body into the bonnet lock.
(Be cautious where you're poking the screwdriver though, it's easy to poke holes in the condensor if you're not careful, as the latch is slightly angled from the lock).