1. Ensure you plug an ethernet cable to a laptop/pc
2. Make sure no downloading taking place on any other devices i.e. tablets etc
3. Run a speed test on speediest.net, I would run this off peak time 8am-4pm and then from 5pm-11pm anytime between those hours, if the speed degrades only in peak times then you could possibly be affected by a utilisation fault (contact 151 for info)
If your speeds is fine on ethernet but degrades on wifi heres a few things you could do?
Log into your router see what operating channel you are on i.e. 2.4ghz if it is set to auto will be on either 1/6 or 11. Every provider runs on the same wifi channels as this is how wifi is broadcast. When you change a channel its best to keep it on a channel for 30mins to get a true reading of how that channel performs with your devices. Same goes for 5ghz test them both out to see which works best for you. You can go to you tube which will show you how to log into your router :-)
If you use Virginmedia's router as a modem only and are using your own wifi router then detach this and run the speed test directly from the VM equipment just as a process of elimination. I understand this can be frustrating but if it helps get to the bottom of the problem then it will be worthwhile :-)
I am a virginmedia employee but all opinions are my own.
Having exactly the same issues, broadband connection down all the time , kids Moaning Netflix won't work on iPads, etc. Have had to go and get s mobile contract with huge data tariff and use that most times with tethering .