Have you checked that it is not you PC causing the problem. I have just manually changed the settings on my computer, family (2x sister and Mother) and a friend who were, between us getting between 6 - 12meg.
Now that are all hitting 18meg + when I spoke to Virgin Media about this they quoted that around 80% of speed issues are due to the config on Windows XP and Vista.
I found out what all I needed on
www.virginmedia.com/help
this is the section you will more than likely need.
http://www.virginmedia.com/help/20mb...timisation.php