When you are doing speed tests are you doing this wired as wireless is prone to interference from many sources.
Can you please post your network stats from the hub Open a Web browser (e.g. Internet Explorer) and enter the address http://192.168.0.1 Note: If you have enabled Modem Mode on your Hub 3.0 you will need to use 192.168.100.1 instead. Do not login but click on where it says "Check Router Stats" and then copy and post from the following 4 tabs, Downstream, Upstream, Configuration and Network logs (if they are pasted then all personal information is * out) and we can check your power level, also while you about that can you please go around and check that all connectors to VM equipment are hand tight. Also while doing this please check for any damage to cable, or un-terminated connection without either coax or a terminator. Also please run "Check service status" at the top right of this forum and call 0800 561 0061 to check for local issues.
I dont work for VirginMedia all opinions are my own. 39 years in IT.