Virgin Media has been using traffic management techniques for some time to ensure peak time downloads do not slow to a crawl. In the near future customers on the Broadband L cable package (4Mbps) should be seeing an upgrade to a 10Mbps download service.
Currently people on Broadband L see their speeds cut to 1Mbps download and 128Kbps upload once they exceed 800MB download or 325MB upload. New rules will apply to those who have had the uplift to 10Mbps, the same download limit applies but a little extra upload is allowed at 400MB and the speeds will be cut from 10Mbps to 2.5Mbps with 128Kbps for the upstream.
The full details are published on the Virgin Media website. The help page details the time period that the measurements are based across as 4pm till 9pm, with the management lasting for 5 hours from the time the limits are exceeded. It is possible Virgin Media is experimenting with other time periods, since one user on our forums has noted what appears to be management during the afternoon.
On a 10Mbps connection, hitting 800MB takes around 12 minutes, and is equal to around three 30 minute TV shows on the various catch-up TV services. Though if using one of the peer to peer download services watch the amount of traffic uploaded, since the point of peer to peer services is that everyone who has downloaded material is providing it to others.