So an interesting turn of events.
I've just got a reply from Plusnet about this issue. (after a week!) Here is their response...
"I have tested the connection and the downstream sync speed is currently 66.4mbps. The workplace profile we have at Plusnet had been set at 63.6mbps due to the last Delta Report from the Exchange which was received on 26/11/2017, reporting a speed of 63.6mbps, so in that respect it was "banded". I have manually increased the speed profile to the maximum, if you now drop the sync on the router for 20 seconds it will update with the new speed profile, and all things being equal you should then see the correct sync speed."
However I've just done that and its not made any difference.
If you want to see my line stats look for .Sam. on
https://www.mydslwebstats.co.uk/Container.htmAny ideas?