The postcode checker seems to have entirely forgotten about FTTC nowadays.
The results that BT posted about their G.fast trials (fibre to the DP) gave some stats about the drop wire (oe lead-in) distance from the DP:
20% of lines have a drop wire shorter than 19m
20% of lines have a drop wire longer than 67m.
500m must be pretty abnormal.
Here's Plusnets final response to my ticket;
Our Support Team have replied to your Question (reference number: 93037992) with the comment shown below.
Dear Mr ******,
Thanks for your time on the phone today. As per our conversation, unfortunately due to the length of the line from the DP (500m) you are not going to see the estimated speeds as these assume you are no more than 50m from the DP.
The testing I've done shows that the connection is now stable as we are no longer seeing the drops we were before the last engineer went out.
Everything is therefore now running as it should (albeit with slower speeds than originally expected).
As agreed I am closing the fault off, but do not hesitate to get back to us if further issues surface.