Is it a Tiscali connection? if it is then Tiscali have issues when certain bandwidth is reached on certain connections - they do something which forces change on their system and this is tripping out the online gaming.
I read this online where Tiscali were apologising about it.
If it isn't Tiscali then it might be the same thing happening so it might be worth contacting the ISP and querying it.
I've never had issues with mine and i'm with NTHell - and that's saying sommat!