I've looked and been unable to find a clear explanation how to remove a front door car with the door locked/closed. But I've also seen reference to garages knowing about the problem getting it sorted with 1 hour labour.

Is this correct; what are the typical costs (plus the cost of a new lock) for a Jag specialist to fix a front door lock that's probably double locked? 1 hour, if correct, is about £100.

Or is there a ridiculously easy trick to getting the card off?

 

First try to get the screw out just belw the handle armrest and the door opener from inside . Do not lose the plastic lid.
then try if you can pull out the lower basket just upwards.
if you mange to get it out there is a plastic screw from below the door card you would have to get loose . Push on it with a hex bit, or cut with a cutter around the clip .have a look at the other sides doorcard first.
then try to pull off the doorcard.
next step is to take out the plastic floor piece then the door seal. There will be two or three more of those plastic lids hidind another 2 or 3 27mm torx to remove the inner plastic door card