Update: Popping the headlight out was definitely the way to go. To anyone reading this thread with a similar issue, it's dead easy to do. Video link i used:
https://www.youtube.com/watch?v=D65x8G1f6AI
My solution was that the bolt I was turning was a bit buggered by a previous owner/garage, but using some Wera hex keys with the round heads and some WD40 I was able to turn that little blighter.
http://www.amazon.co.uk/dp/B009ODV0OE/
In response to "are Xenon's manually adjustable": mine were, luckily! Maybe some models have auto-levelling, but mine doesn't.
Thanks for the support guys (and gals?). This is a great site
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