Went over to Infinity in Jan and all was well until a week ago when the connection started dropping intermittently and very frequently.
This link (https://community.bt.com/t5/Other-Broadband-Queries/BT-INFINITY-wifi-loss-on-MacBook-Air-ready-to-quit/td-p/1160854) gives a solution (message 4). I have tried this and, so far, it is working.
There is also an official BT comment (http://bt.custhelp.com/app/answers/detail/a_id/44798/~/i-have-problems-connecting-5ghz-and-dual-band...) on this.