Slow connection + Ping, but sync speed fine

[#1]

I'm suffering with  strange issue on my plusnet ADSL connection.
Basically, my broadband speed has dropped from 6-odd mbit to 3.5mbit, while ping times to google have risen from around 30-40ms up to 600ms at times, but usually around 300-400ms
I've tried a different router with no change. The ADSL line stats show a solid 8128/448kbs link (as usual) with a solid noise margin.
Here's the results of a number speedtests I have performed recently

BT Wholesale speed test (basic)
Download speed (Mbps): 3.54
Upload speed (Mbps): 0.16
Ping latency(ms): 277
BT Wholesale speed (advanced)
Download speedachieved during the test was - 3.54 Mbps
For your connection, the acceptable range of speeds is 0.6 Mbps-7.15 Mbps.
Additional Information:
Your DSL Connection Rate :8.13 Mbps(DOWN-STREAM), 0.45 Mbps(UP-STREAM)
IP Profile for your line is - 7.15 Mbps
Plusnet esitmated line speed:

Estimated line speed:
    8Mb (Download speed could vary depending on line conditions. Estimates are the maximum speeds that your phone line can support. These speeds are dependent on the package you choose.) - Checked on 2015-01-22 09:33:59
Current line speed:
    7.15 Mb
This has come on the last few days. I have ordered a fibre upgrade if that's in any way connected
Any ideas anyone?

[#2]

Also, I have used both my phone and laptop to check, and have tried an ethernet cable all to no avail.

[#3]

Oddly, I've noticed something the same and I appear to have an almost identical connection to you, resulting in this thread.  Mostly I've noticed the large fluctuations in the evening - is that your experience, too?

[#4]

It does sound reasonably similar yes, but its only come on in the last week or so.
I'll re-check my pings off-peak to compare

[#5]

Just checked this morning and pings are back in the 20-30ms range and speed is back up to 6.5mbps.
I'll re-check during peak time tonight but it certainly seems like a contention/congestion issue somewhere.

[#6]

Mine is also back to 6.74Mbps down with a 17ms ping this morning
I've also noticed it in the last week or so.  Sounds like a very similar issue, both on 20CN

[#7]

Aye, definitely sounds like a linked problem, possibly a failure of some kind on the backhaul back to plusnet HQ

[#8]

I am not aware of any issues.
It would be interesting to know if the problems continue this evening though.

[#9]

I'll check again this evening. Is there any partuclar data you need me to collect or will 20-odd pings to www.google.com suffice?

[#10]

Just try a few please, BBC.co.uk it always a popular test.

[#11]

17:17 today (27/01/15). 20 pings to each host over stable wifi connection.
192.168.1.254 (router as a baseline)
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 1ms, Maximum = 7ms, Average = 3ms

www.bbc.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
    Minimum = 380ms, Maximum = 1110ms, Average = 710ms
www.google.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 325ms, Maximum = 706ms, Average = 511ms

As an aside, pings to google this morning (8am) were around 20-30ms, so it seems to be a contention/peak time issue.

[#12]

19:17 on 27/01/15
Router:
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 2ms, Maximum = 4ms, Average = 3ms
bbc.co.uk
    Packets: Sent = 20, Received = 19, Lost = 1 (5% loss),
Approximate round trip times in milli-seconds:
    Minimum = 969ms, Maximum = 1405ms, Average = 1168ms
google.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 666ms, Maximum = 1226ms, Average = 955ms

[#13]

20:22 on 27/01/15
google.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 741ms, Maximum = 1040ms, Average = 898ms
bbc.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 900ms, Maximum = 1776ms, Average = 1257ms
This is definitely an error/fault condition now. I will re-check in the morning to show the difference in latency

[#14]

22:40 on 27/01/15 and things are better. Still a few high pings, but nothing in four figures
google.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 22ms, Maximum = 220ms, Average = 43ms
bbc.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 23ms, Maximum = 164ms, Average = 43ms

[#15]

22:50 on 27/01/15 and things are back to rubbish again
google.co.uk
    Packets: Sent = 20, Received = 19, Lost = 1 (5% loss),
Approximate round trip times in milli-seconds:
    Minimum = 216ms, Maximum = 674ms, Average = 442ms
bbc.co.uk
    Packets: Sent = 20, Received = 20, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 648ms, Maximum = 1105ms, Average = 904ms