Thanks Orbrey for the reply
------------
BT have 3 available profiles that are made available to the ISPs, which they can change :-
Standard – best overall balance between speed and stability for general internet users
Stable – prioritise stability over speed for IPTV videoconferencing, home workers and businesses transferring data and IPTV
Speed – prioritise speed over stability for online gamers
Its not clear what parameters are set for each of these profiles....
However it would seem (and I stand to be corrected on this) that not all ISPs make use of these options and leave all users by default as standard, and then let the DLM do its thing.
I do know that by default Zen place all their new FTTC provisions on the Speed profile.