That's because someone has pushed the little lever on the boot lock, it prevents someone inside the car opening the boot from the inside, while the spare key is too fat to go in the lock.
It's so when you give the car to someone, you know they can't go through your stuff...it's a neat little feature.
Not so neat when the boot lock buggers up, and you think to yourself "what's this lever" and press it. I had to remove the speakers in my parcel shelf, try and fish around past my subby and click the lock from inside NOT fun!
I sooo didn't read the start of this thread...what a tool!
Dan