Got connected today and am currently using their supplied router.
Apart from a call (with a 20 minute wait) to Plusnet for them to actually activate the connection, it went smoothly.
The BT engineer said it should all be working straight away and as soon as he had tested the master socket (moved into another room) he was out of there sharpish.
So when I got the constant red light on the router, I did a bit of digging online (3g phone connection!) and realised/hoped it was simply a matter of Plusnet flicking some switches their end.....and it was. It came on whilst I was still on the phone to customer support.
I presume the sorting of the line and speed is taking place as my speed test results are varying from 5-9mpbs up and 15-19mpbs down.
Was told I'd get around 76 up and 18 down.
As long as I'm connected, that'll do for the next week or two while it gets tweaked.