Definitely not something on my network causing it. Tested using different devices one at a time and also my router can report the current bandwidth usage of each connected device.
Found out today, from a local Facebook community group, that other people are experiencing the same issue across a number of ISPs (including LLU TT & Sky). Think this must now point to an issue at the local fibre cab.
Edited by mackayd (Fri 21-Feb-20 17:46:11)