Thanks NS. It appeared to do its usual thing whereby the daily spike triggered off a large amount of errors.
I wasn't around at the time it occurred, but when I got back I noticed that web pages were extremely sluggish.
A quick look at DSLstats showed that the CRCs were running at 20,000 per min and the Err/Secs at about 3,000 per hour.
I did a couple of quick speedtests (attached below). I was at the time syncing at a full 79987/20000 and you can see how erratic it makes the throughput.
If you look at the pale green line at times throughput is zero, peaking to 11 Mbps for a single thread. Latency was pretty grim too
So I powered down the modem and it came back up at 73Mbps where its been sat ever since.
Now there is one thing that is REALLY odd. I fully expected DLM to kick in the next morning like it does on previous occasions and apply INP.
But it didn't. Why it didn't I have no idea.
The only possible reason I can assume is that sufficient other people are seeing the same thing OR because we'd had really bad thunderstorms that day, it was attributed as a Wide Area Event.