Before I send you to a JAG dealership
try some wd40 in the trunk (boot ) lock - give it a good soaking and about half hour later use the key from side to side ( do not break it )
If no joy - soak it again and leave overnight - then try again in the morning . if that fails go down to dealership spare parts and ask if he has info and if this is a common problem.
I find in AZ that door/boot locks and window winders & door locking parts dry out and give problems but that WD gets you out of trouble till you can do a proper job to cure problem.