Follow these as well:
At the times you are having issues, do the following
start >> run >> CMD >> ping
www.virginmedia.com
Post the results
2nd >> Whilst in cmd >> tracert
www.virginmedia.com
Post the results
3rd Visit, in your bowser,
http://192.168.100.1. Go to Signal then post both up and down stream.
4th Speed test >
www.speedtest.net post the results.
5th:
http://gamefiles.virginmedia.com/blueyondergames/ chose two files, download them together, post the results.
6th, are you running any kind of router or are you direct to modem via ethernet.
Run all the above results, with both direct and none direct.