Could I add a couple of things which may be import here:

Not all the speed test sites are capable of getting the full speed. A couple which we have been advised to use by Sky as they have the bandwidth to cope on the site are:

  • London : Namesco
  • London : Structured Communications

The next thing which is most certainly worth checking is the computer you are using. I know it sounds daft, but from personal experience this can be a little hap-hazard. I got a mixture of results depending on the computer I used and it wasn't strictly related to the OS or processor in a predictable manner. Also check that you don't have multiple AV programs installed or other multiple products scanning your computer's traffic.

With all this in mind, could I suggest that you boot up in 'Safe mode with Networking'? run the test on the speedtest,net site and return back to normal mode.

If that shows a significant improvement, try going through everything again to see what else you have running in the background. There may well be something else causing an issue. Run some anti-malware programs to ensure that you don't have any nasties hidden away.

I would also suggest running a package such as Advanced System Care. Ensure that you configure it correctly so that it optimises your computer for the faster connection.