This morning and still only 18 hours into FTTC.
Tested on the same wired computer after the overnight period and it's coming out at 72.4Mb from Speedtest.net. Wow!
See here. Looks like whatever was capping the speed has seen the line profile and increased it. It'll be interesting for me to see if the CAB DLM steps in tonight and reduces the line speed or adds interleave. I'm being very careful around the BT Openreach box and following Robertos advice very carefully.
Now my only problem is my LAN is slower than my WAN!
Thanks everyone for all the advice and help.
Tim
Plusnet FTTC