The car is actually a 1987, with the passenger front door closed, presumably locked and won't open.
Door Lock on 1990 Jaguar XJ6
These cars had problems with the door handles wearing out and breaking resulting in being unable to open the door from the outside. The door lock solenoid failed as well. The door panel has to be removed to inspect what is going on (difficult to remove the door panel with out being able to open the door) but its the next step in finding out what is wrong.
1 more answer
I see a door lock relay available from the dealer.