You don't mention how you are connecting to the Hub (From your signature, I see only SH2 in modem mode connected to an Apple Airport Extreme Router on VIVID200) and it looks like you are running Speedtest against a third party (FELIX?)
Does this mean you are connecting via wi-fi? How far away from the Airport Extreme router are you?
Ideally, Virgin should build in a page on the SH that allows a speed test to be run directly from the router out. Would probably solve a lot of 'my speed is rubbish' but being the definitive place to check speed from. That being said, i've noticed that my connection does vary significantly throughout the day.