Can you hear the window motor running when you try to open to driver door window?
If you hear the window motor then it could be the door glass operating mechanism (a door glass regulator - ie the mechanical assembly that is attached to the door window motor).
Here is a PDF file showing the operating mechanism attached to the motor: XJ8 Door Glass oerating Mechanism.pdf
If you cannot hear the door window motor then you might have a bad fuse. I am not sure what fuses you may need to check. Maybe fuse number 15 left-hand door control module.
If you have the XJ8 Vehicle Car manual (that came with your jaguar) look at pages 4-12 thru 4-20 for the locations of all the fuse boxes and the fuses and circuits.
Here is a PDF file showing the Rear compartment fuse box - Left hand heelboard (it is located in front part of the driver side rear seat):
2000 Jaguar XJ8 LH side Heelboard Fuse Box.pdf
Hope this helps.