I have experienced exactly the same issue. Both upload and download speeds have dropped on my BT ADSL line by about 25% towards the end of May 2017. The speeds now achieved are exactly as deefined by the IP Profile on the line. Somehow and for some reason the IP Profile has deteriorated and the line is being needlessly throttled.
This has happened at least three times before but I found that taking the issue up with BT help based in India is a total waste of my time. Once I was lucky enough to reach BT somewhere in Northern Ireland who reset the IP Profile and even called me back to see if the issue had been resolved. That's service.
All I want is the IP Profile to be reset, if not then I'm moving to 4G broadband which is 4 times faster anyway.
Welcome to the forum and thanks for your post! I have moved your post to create your own thread as that's the best thing to do.
Sorry you're having problems with your broadband speed. Now that your conversation is all in the one place, others will be along to offer you the best advice. It can be difficult trying to get advice on an existing thread when there are 2+ conversations happening at the one time.
Firstly here is a graph from SamKnows showing the slowdown in May. I have a SamKnows box monitoring speed 24/7
You'll observe the speed drop from the high 7s to about 5.5Mbps. The Router is connected to the master socket. I have tried the Quiet test and I think that's OK, there's a little static.
Here are the connection stats from the router
SNR Margin(Upstream) 5.2
SNR Margin(Downstream) 2.4
Line Attenuation(Upstream) 20.4
Line Attenuation(Downstream) 40.5
Here is the Speed test via the Wholesale site:
And here is the further diagnostics page with the IP Profile