A relation who lives in the same area,also with tiscali is also having the same trouble!
Are you both on the same exchange? The reason I ask is because Tiscali is one of the providers going into the unbundling market, and they might have problems with their equipment at your exchange. You can check by going to
http://www.samknows.com/broadband/phoneno.php and following the links until you get the exchaneg page where it says "Local loop unbundling presence" and see if Tiscali is on there. Might not be the reason, but it also might explain your problems.
One is just putting broadband into a new house and I am avoiding the providers with an LLU presence in the local exchange. They are cheaper, but I cannot see an easy way to migrate if I have problems. I also have a suspicion of these new LLU operators getting it right when they are all fighting to get as many customers as quickly as possible and no doubt as cheaply as possible.