The trees of Sussex collectively go 
16V means (for a 4 cylinder engine) 4 valves per cylinder (2 inlet and 2 exhaust) the biggest advantage being it allows more fuel/air mixture in and more exhaust out (because a bigger area is opened) so getting more power per cc IIRC especially at higher revs
You also get advantages is spark plug positioning and shorter valve open time which improve power and there is allegedly reduced cam wear but you lose some power as more valve work is required
There must be a Wiki article on it, there is on everything else
You missed a trick Steve, had you told Nick that it was the engine voltage we could have had a laugh in future when he describes trying to get a 16v car battery from the local garage... 

I have failed yet again. Lessons will be learnt, society is to blame
Funny thing is I think his previous one was 12V as a lot of Clios are 3 valves per pot