Thanks for all the replies - all interesting. But to repeat, we've ruled out the geo-targeting / personalisation. We have access to independant machines in multiple locations throughout the UK, and on ones, which are brand new, and not-seen google before.
With regards to seasonal, we've counted for that too. The bits that are new and un-charted is the world cup, and general market conditions.
From all the responses i see above, the ones which i think give a plausable answer is tedsters 'possible' 30% fewer clicks due to the revised layout of google and the fact that the market is currently toilet.
I've been battling search engines for many years now, and 'if' the answer is the new layout, then i've got to say, that this seems to be the biggest impact change i've seen. Yes the algo updates have big effects, but you could always come back to the point that if you get a top position, then traffic will come. However, this may mean that we indeed have to think about the google page 1 real-estate much more intelligently etc