First off this is a great idea and properly executed I firmly believe you could be onto a winner. uSwitch, compare the market, confused etc... they all started like this I bet. that said, I'm about to be ultra picky. sorry.
I like the idea of the images but not the implementation. EG a fairly common car, a Seat Leon, brings back one image of a stock, 2 with a factory optional body kit and 1 with some completely horrendous kit on it. Skoda fabia brings back a Mk1, Mk2, Mk2 with again - another horrendous kit on it etc... Don't look at ford focus
The other issue is image quality - I guess you're pulling back the first entries from gimages but the size of these appear to vary which means you end up with a mishmash of quality, compression etc... just to fit your target area.
If the images were all good examples of the car in question I'd be all for this (and possibly a sponsored link to the website of said car?) but currently the roughness of the implementation puts me off.
I'd consider moving common searches higher on the page. I can see you're trying for a clean look (and I really like it) it's more useful than the other stuff down there. On some sites in smaller text under the search (or above the results) you sometimes see other suggestions or top searches, something like this might work but only if it didn't add clutter to your nice design.
Small stuff
It's possible to search for £0-£0.
If it can't find cars at price £3-£5k maybe it would be nice to auto-populate with cars from the price slightly higher?
Logo is huge and pretty dominating (along with the blue bar), if it was a bit smaller you'd have more vertical space to play with.
Do you really think people will follow you on twitter? Will you be using it? If not I'd ditch the follow link. Infact all the blue bar stuff is fairly meaningless for first time website visitors. If you compressed the top bit more you'd have more space for the results table / less scrolling for your users
"Site" column is left justified, would probably look better centred or replaced with the site logo.
The result table doesn't have the same look and feel as the search part of the site (hard vs soft corners, cell edge colour etc...). It would look better with a more consistent L&F.
favicon/magnifying glass image makes it look a bit like you're e-tyres or blackcircles rather than a car to me personally. Hard to tell it's a wheel from the favicon alone really.