Which speed test - BT, thinkbroadband or another?
If BT, there is an older speed test which sometimes appears when the normal one is very busy or broken. It runs a download of a 1.7MB file.
If that's what you are seeing then the other should return in time. Have you tried the
thinkbroadband one? I found it gives results very similar to the BT one, and you can also get a history and trend graph if you register on the main site. (You can use the same username and password as here).
What you don't get from it is your IP Profile, which only the normal BT one can supply.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost.
Internet connection - O2 Standard.