I have made a reasonable attempt to read through the forums for this problem but can't find anything like it. If I had scrolled right past an obvious solution you are welcome to call me a noob!
When I am connected to Xbox Live my connection will drop any time the landline phone is in use. All of my phone sockets have filters on them and I have no issues using the internet on a PC when the landline phone is in use (the difference being my PC is wired into the router, but the xbox is WiFi).
If anyone has any suggestions I woulld be grateful!