I'd guess it's from models with a spare for the tire iron? An accessory holder for bike rack? No idea.
My guess would be the bike rack: https://gear.jaguar.com/us/en/i-pace/carrying-towing/carrying/t4k1178-rear-mounted-cycle-carrier-lhd/#tertiary-tabs
So I do not think it is the fire extinguisher because the jaguar websiteIf you look at your order sheet, there is an entry "035AA LESS Fire Extinguisher" which I think may fit in that space. Or possible "056BY LESS Warning Triangle."
...I would be surprised if the space is NOT for the warning triangle.
It is the same one used for the F-Pace, E-Pace, XE and XF, so yes you can!