BT one is unlikely, because I can connect to other servers (inc. east.tastysp..) and its fine, as BT is my ISP, it will be using that BT router anyway.. surely?
I'm not sure we can say for sure whether the congestion is on the bt.net end or the above.net end, meaning I think it might be possible the bt.net link to above.net is saturated and so the bt.net router (#13) is responding to pings fast itself, but is experiencing delays trying to stuff packets into a full pipe toward above.net.