I think it can also be in the right hand side in a rolled up tool bag. depending on the model. Mine is a mcs and as said previously its in the left hand side. there is somtimes a first aid kit in there and it could be behind that. Have a good look in there as it can be easily missed if it has fallen flat or pushed up the side. Also lift up the boot panel could be in the battery compartment.
Hope this helps.
The mini mobility system (the puncture repair kit) is in the left panel as Mini One is NOT supplied with run flats. There is also a pouch which houses the jack in the boot, but no sign of the wheel nut adaptor.