So might be worth checking if the problem started around the time you may have plugged in a new bit of kit.
I did wonder if this might be a possibility, however there has been no new kit installed anywhere in the home for ages, certainly not since I moved to Sky back in November and the connection was OK up until end Feb / early March.
The Level 3 engineer I have been speaking to has pretty much said that based on his experience and the type of errors that are manifesting, it is almost certainly a cable problem. The copper has been in the ground since the place was built 50 years ago so degradation of the conductor / crimp is highly likely.