Fluctuating speeds?

[#1]

I've never had speeds fluctuate so much as I have in the past couple of months...
Used to get around 7mbps, and now getting between 5 and 1?
Also ping never goes below 60ms, when we used to get around 30ms?

Not sure if this is the right section, but it's sure as heck annoying.

My router currently shows these stats:
ADSL   
  Type Interleave Path   
  Status SHOWTIME   
    Downstream Upstream
   
  Data rate(Kbps) 8128Kb 448Kb
   
  Noise Margin 8 21
   
  Output power(dBm) 123 199
   
  Attenuation(dB) 31 18
   

Anyone got any ideas on what we can do to make it like it was?

[#2]

Hi Mark,
I can see that your connection dropped just after midnight on the 20th but it hasn't altered your connection profile either on BTs or our side - both are still set to 7150, so there shouldn't be any slowdowns from that.
I realise this is a bit out of left field but would you be using a combination of ZoneAlarm and AVG by any chance? We had some reports near the end of last week that this was causing network connection slowdowns following one or both programs being updated. If it's not that, please post some speed test results from http://www.speedtester.bt.com and we'll be able to investigate further from there.

[#3]

Hi Matt, I use neither AVG or Zone Alarm.
On the PC's I have running Windows, I use a combination of Avast! and Windows Firewall.
As requested, I have posted some BT Speedtester results, although I have requested my MAC Key and will be leaving PlusNet in the near future.
Thank's for reading!
Download speedachieved during the test was - 2183 Kbps
For your connection, the acceptable range of speeds is 600-7150 Kbps.
Additional Information:
Your DSL Connection Rate :8128 Kbps(DOWN-STREAM), 448 Kbps(UP-STREAM)
IP Profile for your line is - 7150 Kbps

[#4]

Hi Mark,
Its up to you but we're happy to investigate this issue for you to see if we can get this resolved between us and our suppliers as the throughput speed clearly is no where near the sync speed here which means that you would most likely still have the same problem if you were to move to another ISP.
If you would like to proceed an give us the opportunity to look into this for you we would just need you to follow this link and complete the fault checker form:
https://faults.plus.net