Well, I don't even from UK, so I don't know if my experience will be someway relevant for you
I live in a pretty bad area for ADSL (the telephone cables here is more than 10 years old and I never see any routine maintenance, just if something really fail)
Fortunately I'm close from the DSLAM, like 1 km, but my att is 32, maybe because of the age of these cables...
I'm testing a 3 snr target for 3 days and all is going fine until now (there is a lot of Super Frame and HEC errors, but no forced resyncs at all)
My actual stats:
I made a modem restart 2 hours ago to try some others tweaks to reduce the errors, but had no success. and I think it's because the line is much closer to max attainable Line speed
9184 is my line cap, so I can't get more than that anyway
I have chosen ADSL 1 (G. DMT) because I get a way better ping in this mode, like 19ms vs 50ms from ADSL 2+ with 64 bytes of interleave
The modem shows my G.DMT line as Interleave, but in fact there is not Interleave at all
Speed test:
I tried to make this text the better possible (even used a spell checker, but English is not my best language)
btw i'm from southeast part of Brazil.