OK, so whilst filling up the bike on the trailer to go to track day, I also filled up a fuel can, after filling can I placed it in the boot but did not fit the 'aircraft style' filler cap
As you'd expect, it wasn't where I left it when I went to unload the bike
Luckily a mate had a spare complete Honda filler cap with key to get me out, but obviously I had to give it back.
Annoyingly there were others there with similar aircraft type fillers and I must've tried every one and they all had different threads to mine
Luckily There's no name brand on the tank part so I haven't got a clue who made it!
Probably not a mistake I'll make again