sometimes you've just got to keep badgering them to do it properly 
After almost 3 months of to-ing and fro-ing with LLU provider, they've had BT out now 5 times to my fault , and it looks like today may have finally done the trick (fingers X'ed, touch wood, etc.) and changed the pair from exchange rack to entry point (but without the lift & shift that last OR bod recommended). Am now monitoring performance to see if it's fixed or not, but the point being you need to keep on at them (ISP,BT, whoever) if it's still not right....
My ISP (Zen) has been brilliant and the BT engineers have been really good too. You get to speak to proper people at Zen rather than Mr Script in Gawd-Knows-Where and I haven't had to do any badgering. Apart from the fault itself, I'm happy with the progress made trying to remedy it. I need to find out what's causing the fault for "certain" reasons (hint: it only happens a few weeks after I start to live at that house again), however if it proves just to be a fault, I'm going to bail onto Virgin cable after all this.
At the moment, were down to badness being someplace between my house and the green cabinet, which is only a few hundred metres down the road.
I spoke with an ADSL person I know yesterday and he explained the whole set up to me and I can see how low frequency interference would cause sound to come through the phone, as well as the fall off in the download channels and all that.
All in all, trying to get this fixed could be a lot more hard work than it's been so far for which I'm really grateful. Imagine if I was with Tiscali for example!