Frustrating but interesting speed issue

[#1]

On Friday, we had two power cuts. Following these we had no broadband and crossed lines on the home phone (both with PlusNet). A fault was identified on the line outside the house, which was mended on Sunday. Since then, my router, a Billion Bipac 7800dxl, has reported incoming speed to the house in the range 1.9 - 2.2 Mbps, which is our standard speed. However, with wireless switched off at the router, and only one wired connection to a Windows 10 desktop computer, BroadbandSpeedChecker reports speeds in range 0.04-0.09 Mbps. I have swapped the router to a BT HomeHub, in case the Billion had been damaged, but the same was the case with the HomeHub.
My initial thought was a background download, but I can find no evidence of this. I have tried diagnosing the network connection, and resetting it, plus numerous reboots, but all to no avail.
Does anyone have any suggestions please?

[#2]

can you test it using a different machine wired into the router?

Have you tried different speed testers?

http://speedtest.btwholesale.com/

[#3]

There was a massive Win10 Fall Creators update today for many of us.

[#4]

Testing your line is showing it's connected at around 2Mb/s, however the line is showing a very high number of errors. Can you ensure the router is in the master socket, with no extension leads in place please. If you dial 17070 from a handset do you hear any noise on the line?