Well, this has happened to me - I have been deemed a "Heavy Internet" user - with a whopping 5.04GB od data passing from the web to my computer in a month ( period 5th Sep to 5th Oct ) my connection is now a whopping 300-40kbs a sec.... i am on the 10mb connection...
After an hour long conversation of them not being able to tell me why i am being traffic managed - due to all the figures they give me being a really low download, considering I play games online, they have said anything over 1.2GB a day in peak times will instantly get me throttled.
Great news. Anyway after very long and not very fruitful conversation with their call centre, we have told them to stick it up their arses and getting the whole thing ripped out - Telephone, XL TV & Broadband - I am not paying 25 quid a month ( I am not giving them over a grand of my money a year to be tricked ) for a poxy speed to be talked to like I have done something wrong, I challenged them and they couldnt give me adequate answers. so they can F off.
Good luck Mr Branson...
http://www.virginmedia.com/help/traffic-management.php