Question Author
Thanks for all your responses.
I managed to get into the boot eventually - the keyhole and mechanism was jammed through lack of use. Turned out it was a flat battery so recharged it and problem solved.
To answer your suggestions - our breakdown service doesn't cover home and you can't get into the glovebox to read the manual as that's electrically operated as well!
However, having found the Jaguar Forum there is apparently a special point somewhere under the bonnet which allows you to jump start the car without accessing the battery.