http://bt.custhelp.com/app/answers/detail/a_id/10495...
5. What is BT's policy on Peer-to-Peer (P2P) applications?
P2P refers to certain applications that enable files and program sharing between groups of people logged on to a P2P network. Because they use uploads and downloads and are often left running 24/7, they consume significant bandwidth, even when being used by just a small number of customers.
Because a lot of P2P traffic is not time-critical, e.g., downloading and uploading TV programmes or movies for later viewing, we treat P2P traffic differently from time-critical traffic (such as surfing, streaming or internet telephony) and apply speed restrictions to all P2P traffic. We manage these restrictions daily based on the demands on the network, but downstream restrictions will typically be in place 4pm - midnight on weekdays and 9am - midnight on the weekend. Upstream restrictions may be in place at other times.