Solved, and car MOT'd yesterday.
It was the wiring coming out the bottom of the fuse box.
"I think it's this purple wire"
*gentle pull*
"Yep, the one that's come off in my hand"
A bit wire and some solder later, problem solved!
ps. Sanjoy, I also switched it out with the arch liner still in, the bolts holing my arch liner on are orange and round, and I couldn't be bothered finding my mole grips
Thanks guys
Chris