Have you tried a different Ethernet cable to rule out a damaged/faulty cable?
If you go to http://192.168.0.1/ (or http://192.168.100.1/ if you are in modem mode) to get the VM hub GUI. Don't login (unless this is your first visit to the hub GUI, which does require you to login) but instead click on Router Status which is a text link at the bottom of the screen. Click on the Downstream, Upstream and Network Log sections and copy & paste the figures from those screens and post them here, don't worry about the formatting or you can post screenshots if that is easier. If using screenshots be careful to edit out or obscure any reference to your WAN IP or MAC address in the log to protect your privacy. If you copy and paste the log then the forum will automatically censor this sensitive information. Also note that images will take time to appear on the forum due to a combination of awaiting moderator approval and buggy code.
The community can have a look for you and see if anything in the figures looks wrong and advise accordingly. Or you can wait for the VM staff to pick up this thread (may take a few days) and run checks on your line.
My setup: VM TV box, M350 Fibre broadband with Hub 3 in modem mode connected to a Netgear R7000 router. Telewest/VM user since 2001.
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