Virgin Media has been throttling P2P upload speeds as part of a trial of a new traffic management system.
"After the successful out of hours trial of our combined upstream and downstream file sharing traffic management policy, we will be trialling this new policy between 17:00 and 00:00 (12:00 and 00:00 at weekends) for one week starting on Wednesday 2nd of March," the ISP said in a post to its forum.
"Between these times, P2P and newsgroup upstream traffic will be managed in a similar way to our current downstream traffic management. If the trial is successful we'll launch the new policy immediately."
Virgin asked for online gamers to offer feedback on how the restrictions affected gameplay.
"Well I'm used to the slow speeds on Virgin, but yesterday was abysmal, as in I was gonna write a nice long reply.... but the internet was so bad it took 15 minutes to load every forum page and half the time cut out.... funnily enough starting exactly the same time your trial took place," said one user, known as STARSBarry.
Meanwhile, a user known as Dirrt added: "This has not made my gaming better, this has made it a LOT worse. I play Rift, and was fine in-game until yesterday - the lag is incredible, and the game is unplayable, thanks to this ridiculous P2P throttling."
The ISP revealed that some of the Rift traffic had been misclassified by its servers but the problem had been resolved. However, several users also complained about the effect of the traffic management system on World of Warcraft.