Occam's Razor: the most likely explanation is often the simplest.
And this one happens to be stunningly simple.
redlion: some of your links contain what appear to be user session hashes (which is DEATH to any SEO campaign), definitely contain IP addresses (which I've never seen before, but I'd put in the same class as user session hashes), and an "affl" querystring which Google may well be interpreting as "affiliate marketing" (and sites that do this traditionally don't get much love from The Goog). There are exceptions to this (e.g. Amazon) but for the most part, this holds true.
If you need to use session variables to process information (which for the most part, you shouldn't), use them the way they were originally intended. Store the session variable on your user's machine and read it from there, instead of putting it into a querystring. The same logic goes with the IP address. If you can read it, you can read it and use it any time you want.
You may also be hurt by the TradeDoubler banner (the most useless concept in online marketing) on the bottom of the page.
And all of this leads to my ultimate point:
http://validator.w3.org/check?uri=ht...ports.co.uk%2F
You've got a buttload of validation errors happening, most of which relate to the stuff I already mentioned above.