JSme

Ok, so
 
Stripped the trim so I could pull down the corner of the headlining.
 
I could then see the back corner drain for the sunroof. I doubt you could see it without loosening the headlining.
 
I sprayed some water on the sunroof and could see the drain tube dripping where the blue hose joins a white connector, which then connects the metal drain.
 
So I siliconed up this joint, then PTE, then some gaffer to be sure.
 
Then re-sprayed to find the joint being fixed, but water was now coming over the top of the drain, I felt around and there was a weird little nut in there, blocking it all up!
 
So joint resealed and nut removed, I dried everything and checked again, all sorted and draining nicely out of the wheel well.
 
Phew, hopefully that's it sorted. Thanks chaps.