and are only sent in exceptional circumstances, but they do get sent.
If you are in the habit of downloading films and/or MP3 music files via Peer to Peer servers you may well exceed what is considered to be a fair amount of bandwidth. This will impact on other people who are connected to the internet via the same 'gateway' as you; in effect, you'll be a bandwidth hog, and your ISP will take steps to stop you. They'll do this by warning you, then by charging you for the excess, and finally (in extreme cases) by disconnecting you altogether. "Unlimited" in this context does not mean "without any controls whatsoever" if you aren't playing fair.
Apart from hogging bandwidth, if you're downloading copyright-protected music/games/software/films via P2P sites you are also breaking the law, and in some circumstances you may find that Tiscali will report you to the relevant authorities - you could conceivably be prosecuted, and face a large fine.
Don't ignore Tiscali's warning - they mean business, and they will act to stop you if you carry on.