Presumably it’s legal, otherwise JLR may have a massive recall on their hands?!? The MOT page says lockable fuel cap.
I think the fuel filler CAP is the round plug that you rotate counterclockwise to remove, and clockwise to “lock” into position, as per the MOT.
So it isn’t a security lock (to prevent fuel theft) as such. Instead it’s just a mechanical ratchet/click that requires deliberate force to open (a bit like a child-proof bottle lid) and stops the cap slowly loosening due to vibrations?
Whereas fuel filler FLAP is the painted flap on the outside of the car, and is electrically lockable on all PHEVs, and some lucky/earlier other models?
Jaguar Owner Information
“When replacing the filler cap, turn it clockwise until the ratchet clicks.”