This link will connect you to BT Wholesale's broadband speed checker ... follow the instructions and close any open programs (including those running in the background, like anti-virus & firewall) and then click on begin test and away you go.
If it prompts you for a user name and password they are:
User Name: admin
Password: password
I have noticed that it doesn't always require password login
http://speedtest.btwholesale.com/