ruraldev wrote:
... but when the BT hub is connected the Netgear just shows 1 MAC for 192.168.1.1

But it could just be, that the BT Hub doesn't bother with the 'sanity check' that its IP address isn't already in use. (When the Vigor asks the question (via ARP) and something answers, the Netgear will hear that answer too.)

No idea, it's getting a bit beyond my knowledge of how these things work, I just assumed that the netgear would check the network itself.

UPDATE

It turned out that it seems to be a Netgear switch which caused the issues, after disconnecting almost everything I have I found that removing the switch solved the problem.