unlimited is as much data as you want there is no limit but p2p may be restricted at peak times if you took your contract out before 1 Feb 2013
If you like a post, or want to say thanks for a helpful answer, please click on the Ratings 'Thumbs up' on left hand side. If someone answers your question correctly please let other members know by clicking on ’Mark as Accepted Solution’.
BT do not alow you down for using too much data. "Unlimited" really means unlimited. If you're not on an "unlimited" package, BT still won't slow you down, but they will bill you for the over-usage.
Unless you are on one of the new "totally unlimited" packages, all P2P communication is throttled heavily at peak times. BT do not intentionally slow anything else down, but there may be congestion on the network that makes it look like they do.