Hi Andy,
You're having the same issue I am. I'd advise you to start the complaints process ASAP because Virgin already know about this problem and they are doing sweet F all about it. It's affecting a huge number of customers around the UK, not just you.
Open an official complaint here: https://www.virginmedia.com/help/complaints
That will at least give you a reference number to bring up, that's the only way to get past the "turn it off and on again, are you back online? Well then it's resolved goodbye" stage.
After 2 months you can bring it up to the Ombudsman. Seriously, take a look around the forum and you'll see that this issue keeps coming up. They bring people into DMs to make it look like they're dealing with it, but I assure you that they are not doing anything to fix this right now, and you're not going to see this resolve itself.
Make a complaint to OfCom too if they keep blaming it on WiFi: https://www.ofcom.org.uk/complaints
