For the benefit of my fellow members, i have an update on this.
After receiving a replacement router and setting up as per instructions. i re-ran the tests again and there was no improvement.
I was a bit disheartened and almost resigned to having the slower speeds. As a last ditch attempt, i re-ran speedtest.net in Internet Explorer (i had previously ran it in FireFox).
This was the result:
The result was confirmed with running the BT wholesale speed test in Internet Explorer also
So, i feel a little foolish - i was getting the speed i was supposed to be getting but Firefox was causing false speed test results - especially with flash based speed test sites.
My advice to my forum members is to use IE to run speed tests in the future or even use non flash based speed testers such as
http://speedof.me/Hope this helps someone!
Rich