My initial setup before any of this happened was router to tv on a 3 meter extension. Had this 5 years no issue. This fooked up engineer coming out had to doctor things a bit. So have 2 on the go atm. But this is only since these issues started.
I would remove one of the routers immediately. You only want to be using 1 router full stop.
Plug the brightbox into the master telephone socket. That's where it needs to be.
Do not use an extension cable from the master telephone socket.
Never use anything like this
http://www.digitechworld.co.uk/ebay/images/fullscree...
You need to get a longer ethernet cable from the router to the TV. You can get that on ebay for about £1 to £1.50.
http://www.ebay.co.uk/itm/High-Speed-RJ45-Ethernet-C...
Your setup needs to be Master socket - filter - router.
The filter must be the first thing connected to the telephone socket.
NOT LIKE THIS master socket - extension - filter - router (this may cause issues) - & is how I suspect it was.
Then your setup will be perfect.
Did you do a speedtest with it wired?