Thanks for the Private Message.
I have passed your availability over to our Network Team and I will post back on this thread to confirm the date and time of this visit.
Engineer has just left after spending nearly 3 hours on the problem.
Now fixed (ac balance problem apparently) and syncing at 23 Mbps down/ 6 Mbps up so I am a very happy bunny.
Thank for all your help and to the network team for so quickly arranging an engineer vist.