Extremely low speed issues past few days

[#1]

Hi
Our speed has dropped considerably the past few days, at all times during the day.  Router is usually on 24 hours a day, have tried leaving that off for 20 mins etc, but the same.  A few other people in our village saying they have the same issue.  BT speedtest is showing this:
Download speedachieved during the test was - 172 Kbps
For your connection, the acceptable range of speeds is 600-7150 Kbps.
Additional Information:
Your DSL Connection Rate :4672 Kbps(DOWN-STREAM), 448 Kbps(UP-STREAM)
IP Profile for your line is - 3500 Kbps
You can still browse to some degree, but video streaming etc is a no-no and my kid is getting extremely annoyed at that 😄 
The internet light has gone red a few times on the Thomson router we have.  Getting a high amount of FEC errors on downloads, 49k of them over a 20 minute period.  There's no point even trying to download any files, even if they're just a few mb, since it times out and fails.
We're on the 01542 exchange.

[#2]

Ran the final Test on the BT speed test site and it's saying this:
This Last Test comprises of Best Effort Test:  -provides background information.
Download  Speed
50 Kbps

0 Kbps 7150 Kbps
Max Achievable Speed
Download speedachieved during the test was - 50 Kbps
For your connection, the acceptable range of speeds is 600-7150 Kbps.
IP Profile for your line is - 3500 Kbps

Your service was found to be performing poorly. Please raise a fault with your service provider, stating that the BT Performance Tester tool indicates poor service throughput performance after the third test.

[#3]

For the purposes of elimination assuming you have one of the newer BT master sockets can you connect the router into the [color=red]TEST socket within the master socket, you get to it by removing the lower faceplate and unplugging the part which has the house phone extensions, if any, connected to it.
It would be useful to try another router wired to the PC if possible to eliminate any issues with the one you are using, is it a  v7 or v8?
It may not be relevant but try this checker and see if it flags up any issues at the exchange.
If you still have the same problems after doing this then you will have to raise a "fault" with Plusnet.[/color]