Hi all. Just an update on this, should it be of benefit to anyone in the future. I've had a very knowledgable BT engineer over yesterday afternoon and again this morning and after upgrading a number of things on the line, there appears to be a considerable improvement! The one thing that remedied the unstable noise margin was a new D side pairing at the cabinet (I think that's what he called, you more knowledgable peeps can correct me if I'm mistaken!) Immediately this led to a considerable increase in speeds and a nice steady SNY margin graph! This also improved attenuation of 69.5dB to 67.5 on the downstream which was most beneficial!
He suggested that I stick with a 9dB profile given the length of the line. I have tweaked this via the modem and I'm currently synced at a 7dB margin with a connection speed of 1778 kpbs. I will leave it at this and see how it fares over the next few days. Throughput is around 1.5 mb so much better than the 0.9 that I had previously. He says as with anything broadband, this may last for a long time or may only last a few days but kindly left his number should a problem arise again in the near future.
Hopefully I won't have to go out hunting with an am radio after all, but we'll see!
Thanks everything for your input, it was all greatly appreciated. Let's hope these improved connection speeds last!