Tiscali Wholesale provide the following test login for their datastream based services (BT test log-ins, including whatever@speedtest_domain only work on IPstream)
The test log-in will connect you to Tiscali's network, rather than routing your connection on to your ISP.
Access is restricted to the following pages:-
http://speedcheck.ispconnect.co.uk Open this page to run a speed test.
http://www.dslconnect.co.uk/ this displays a test page (often doesn't open)