Thanks for the suggestion. The exchange was actually upgraded to ADSL 2+ a good while back, and the recent upgrade has been for FTTC. Whatever they did during the upgrade caused chaos with my connection. However, it returned to 3.5Mbit yesterday and so far it seems stable, though I haven't been online much to check.
It looks like it might have been a temporary problem after they installed new equipment.
fttc would only really have any chance of affecting you if you were at a headend exchange.
it may have just been coincidence, could have been a card change or maybe even a full card reset by the owner. a whole range of things but im glad its ok now.
i dont think the installation of fttc would have any sort of effect on existing adsl,adsl2 services.
these comments are my own and in no way represent any company that i may or may not be linked too.