Tiscali's denied it's blocking CoD4 play deliberately, following news that the ISP wasn't allowing P2P connections at peak times. The shooter uses a P2P system for game-matching and is therefore unplayable for those with Tiscali connections during the evening.
“Reports suggesting that we were deliberately blocking specific games are incorrect. We are constantly working to upgrade and refine our network to ensure our customers can enjoy their favourite applications,” said a spokesperson here. “Work is currently underway on routine updates and we will keep you informed.”
Deliberate or not, Tiscali has something of a "situation" on its hands. Check out this 42-page forum thread written by Tiscali-using gamers to see what we mean.