Nice theme, colors work well and not too cluttered which can often be the case with car websites. As for getting higher in search listings, carry on what you’re doing as you have a good number of links. You’re in a very competitive market but focus on building links using the anchor text you want to rank for. I’d think about changing the title tag of the page depending on what you want to rank for - “Motor Depot Car Supermarkets | Home” could be altered to include the main keywords. The title tag is your main on-page SEO factor. You have a blog hosted at blogspot which is good but I’d consider moving it to your own site, eg at http://www.motordepot.co.uk/blog. Your blog has around 9 thousand links to it, I’d have put the blog on the actual site to benefit from all those links.
What are the terms you want to rank higher for?