Hi Wardy
A quick check on opensiteexplorer comparing your site and the number 1 current ranking [<cite>broadbandspeedchecker.co.uk</cite>], the results show a huge difference in inbound links, page authority, domain authority and social activity to name a few.
You said so yourself that your domain is only 12 months old. Doing a quick search on Google.co.uk indicates that there are about 23,600,000 results for the search phrase "broadband speed test". Fairly saturated market but time will hopefully allow you to improve.
The fact that your site is at the number 10 position is not bad in my opinion for such a young domain. Get your new site uploaded with 301 redirects in place and review it after the new site is up and running.
