Have you tried the BT test account - not sure if it works with Tesco connections, but it does with most.
Use the username bt_test_user@startup_domain with any password - you wont be able to view webpages, but should be able to connect to your local telephone exchange.
Thanks Demon for the info. I have been having trouble connecting to UK Online for weeks (see other thread). I have rung Technical Support and done everything they have suggested but no result. It can take me up to 10 attempts to connect but I have used your tip and that works ok everytime. I guess that puts the ball back in their court if I can only speak to them!