Climb in yr boot armed with a pozi screwdriver and a torch, remove screw from centre of handle on the boot plinth and the plinth will then pull off. Bang in the middle behind the plinth is thin steel rod running top to bottom, pull it up and SHAZAM, the boot is open.
Like said before, source yaself a new barrel with key that works, remove the thin steel rod from the back of the button, you then need to remove the push button and barrel as one, its held in by two clips on top of the button inside the boot that are a little awkward to get to, push the clips down and then the button out, reverse procedure to refit new button and put yr boot key on yr keyring
