I've been having issues with varying speed for months with VM broadband - it's rarely (but on a few occasions) been unusable, so I've been living with it. I'm on the M600 package and most days, can average around 600 somewhere.
However, over the past week or so games with friends have become almost unplayable and my speed fluctuates wildly anywhere between 200mb and 650mb. I lag everywhere - it doesn't matter if they're hosting or I am, same issue. This has been confirmed in multiple games.
Over the past 24 hours I've been running the Broadband Quality monitor and it's showing huge latency spikes and some packet loss - they've calmed down over the past 10 hours or so but that was overnight.
I'm on a desktop pc and I'm wired directly in to the router with cat 6 cable.
Things I've checked/done;
Factory restored the router, multiple times
All coaxial connections are connected properly and tight
Only one wired device (my pc) connected, no loose ends
Virgin are just oversubscribed, and haven't bothered to increase the capacity of their network. It's been like this for over a month for me, they keep promising it will be "fixed soon", but I've yet to see any improvement and am starting to consider new providers.
While you're most likely right with over subscription, I hope not as I'm out of contract in just over a month and wouldn't have a hope of getting it fixed by then. Might end up having to look at new providers.
Have just tried ringing up to speak to somebody - went through the fault route and it ran some "automatic tests" which just said "it looks like your router needs restarting", then advised me to come to the forums if that didn't work and hung up!
I have the same issue like you. And I've had both cables and router swapped by engineer and still have the same problem 😂😂 so it's over utilisation problem... They keep selling without upgrading and now lockdown and everyone is working from home and stuff. They will just run around their trail rather than admiring it because they have to give you a discount 😂😂😂😂😂