welcome to the forum
did you get an email from BT recently advising that your exchange was being upgraded to 21CN?
You are now on 21CN adsl2+ which is quite aggressive if there is noise present on your line. Your current noise margin is 34.8 whereas normal is about 6. Have you been having disconnection problems with router resetting and/or have you been resetting the router hoping things will get better? Are you connected to the master socket or better the test socket?
there are some interesting illustrations here http://www.jarviser.co.uk/jarviser/homehubindex.html