Hi Simon
I currently see your homepage ranking in 30th position on a Google UK non-personalized search.
Rankings do fluctuate constantly, there are so many factors as to why they do, such as different data centers, different locations, constantly changing strengths and weaknesses of sites, just to name a few.
As you are still ranking on the 3rd page and appear to have over 4,000 pages indexed by Google, I very much doubt you've been peanalized in any way, a penalty would cause your rankings to drop further than from the 2nd page to 3rd page.
Try searching again, from different browsers, even different locations, try exact and broad searches. Chances are you'll see your site coming up again as it is still there.
Hope that helps,
Regards
Simon
