I'm going to answer my own question now:-
Just had a chat with a new member 'PeteB'. He is a VAG technician, useful guy to have on the forum
. Apparently its a temp sensor for the MFA and he's seen it fitted to the Mk2, not seen it fitted to the Mk1. Still not quite sure exactly where its meant to be fitted but I'm sure I'll find a place for it with a little further investigation. Anyone out there with a campaign edition Golf GTI? I'll bet thats got it fitted. It'll be somewhere near the O/S front wing, headlight, indicator area.
Whilst I had the bumper and spoiler off thought I'd give it a bit of clean up. Its come up really nice:-
See that wire looped around the bumper attachment/chassis hole, thats that sensor