Massive fibre speed drop ??? 80mbps down to 20mbps???

[#1]

As above, got fibre 4 weeks ago....regularly getting 75 to 80mbps....wonderful I thought. ...Unit the last 7 days....its dropped woefully...in fact it has got worse again today...12mbps ....
Tried reboots of the router / modem...to no avail. Also tried the diagnostic tests....no improvement.
Nb* Did notice some engineer activity at the box at the bottom of our street ....coincidentally on the day the issues started.

[#2]

Hi Claire
If you last diagnostic test at BTW tester was showing a red bar then I would log a fault if I was you at http://faults.plus.net

Please do not run any more BTW tests as Plusnet can only see the result of the last one and you want them to see how bad the speed is.

[#3]

The connection rate between the modem and the cabinet looks fine, there are no obvious faults that I can see. If the speed continues to be low then I'd suggest going through the faults process that georgelnx has provided.

[#4]

*****SPOILER ALLERT*******
Welcome to SLOW FTTC speeds. When I was on copper cable I was getting 16megs download speed [max speed 20megs]
Now on FTTC I get 20megs [max speed 40megs].
Before anyone tells me you cannot get the max speed I accept that but when PlusNet told me last year that my phone line should get between 32.5 - 36megs and I get 20megs I find that hard to accept!
Plus net slogan should read "We'll do you"!