how to open trunk without key
Since you ruled out the logical solution try a crow bar or removing the rear seat.
I think there is a button to unlock the trunk from inside the car. It is either on the dash, left side, or in the glove box.
There is latch release under the left side of the dash
Looking for a Used S-TYPE in your area?
CarGurus has 376 nationwide S-TYPE listings starting at $2,000.
Search Jaguar S-TYPE Questions
Jaguar S-TYPE Experts