The TPM seems to have done the trick and my BQM is now a very different looking thing:

http://www.thinkbroadband.com/ping/share/1c294b6d6f6...

No latency and no high pings since the TPM was completed on Thursday afternoon.

Well that's good news then Dom, and all in all, nothing a poor old engineer could have identified or requested to be done. How did Plusnet get round to requesting this for you ?

On the plus side, having your house wiring issue sorted has produced a nice speed increase

After the lift and shift hadn't helped, PN escalated things back to BT wholesale who initially rejected the TPM requests several times. When BT said that they suspected SHINE (and then REIN), PN rejected those suggestions and pointed out the history of the issue and the top quality work of one BTO engineer who'd investigated REIN in September. BT then agreed to arrange the TPM.