Im having the same problem with my connection, and have posted in the support newsgroup, being told that I have noise on my line in the evening, Im from Manchester...which assuming your name, you could be to. Im in the M43 area and my connection is unuseable in the evenings.
I would try posting in the newsgroup, customer support are there up to 10pm and will look at your query for you.
virginmedia.support.broadband.cable
http://www.virginmedia.com/customers/newsgroups/