From what you've described its over utilization. I'm assuming you get fine speeds morning/after midnight?
If it is Over Utilization then its usually a fairly long wait (~1-2 years) for a fix.
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I also live in Wakefield and have been having issues since I signed up for Virgin Cable back in September. I have the Vivid Gamer 200 Package which is supposed to see speeds of up to 200Mbps but I'm yet to experience what that feels like. I get around 10Mbps down and that's on a good day. Not to mention how irritably poor the customer service team are.
Over-utilisation is apparently the cause in the my area, even though I was told during the sign up process that, with the Vivid Gamer 200 package, my speeds will not slow down. I'm paying a lot per month for a service that cannot be provided.