Fibre Extra speeds at 20/0.5, link speed is 70+/20 - what to do?

[#1]

Having seen a drop in performance recently, I ran a few speed tests (BTW and whatever the default Google is).  I'm consistently seeing 20/0.5 instead of my usual 75/19.  The BTW further diagnostics tells me I should be getting about 74/20

I unplugged the audio circuits, turned off the wireless connections at the router, plugged in one PC, and rebooted.  Same numbers.

Recent history: re-contracted in early July; nearby thunderstorm in late July (which took out a phone).

Does anyone have any suggestions?

TIA, Stephen

[#2]

Plusnet support suggested I pull the front plates off the BT connection and try a different microfilter.  I think I threw all my microfilters out with my SCART cables, so they are sending me a new one.

I found a straight through adapter.  No change, still 20/0.5.

[#3 · Accepted solution]

A visit from Openreach diagnosed an underperforming modem.  I scoured the house for a Hub, swapped it, and speeds are respectable again.