Mine did exactly this about this time last year. I found the latch was too hard to move using my hands or tools as its designed (i assume) so you can't quite get a screwdriver or something similar in to prise the lock open.
What i did in the end was pop the bonnet and prop it up as far as it will go with a bit of wood or similar. Then i fed some string through the hook on the top of the secondary catch and fed both sides of the string back over the passenger wing and pulled. I had to pull fairly hard but it worked after a couple of minutes of tugging. Turned out the cause was my lock was seized up, a good clean and some WD40 and touch wood its been fine till now!
My little black plastic catch pull thing has never been quite the same, it doesn't spring out anymore but that doesnt bother me as long as i can open the bonnet!