Broadband speed up & down

[#1]

Thought I would post an up-date. All the comments lead me to believe my laptop was at fault and that my line was stable. I spent about a week tearing my hair out. Received an e-mail from Plusnet today :-
Dear Mr Gibson,
Ive tested your line and can see there are some automatic settings on your line which are could be causing problems on your line and your speed youre able to get on the line can be affected as well as stability.
This has been caused by the exchange you are connected to trying to cause the line to over perform. This has caused instability of the line which then causes data loss and speed problems.
Ive arranged for the line to be reset to try and fix this. The reset normally takes 4 hours to complete. After 4 hours if you have not seen the speed increase already, your router will need to be powered off for 10 seconds and then turned back on. When it reconnects we"d expect the speed to be normal again, but it can take 24 hours before everything fully updates.

Not bad. 11 days to let me know this !!!

[#2]

Hi there.
It looks like your SNR target had dropped to 3db which will have been causing issues.
I can see we've reset the line to increase it and we've also done some modifications to your line to prevent the issue from returning.
Fingers crossed this has done the trick for you.
If you have any further issues please let us know.

[#3]

Really? It certainly looked like the only problem was with the laptop wireless, with the other PC getting good speeds, and nothing in the DSL stats to suggest that the low SNRM was too low or that there were too many errors.

[#4]

Bob,
ejs has said what I was thinking.
If you have two devices using the same internet link and one delivers 9+Mbps and the other substantially less and they both use the same router WiFi link then the difference can only be down to each device's hardware performance or WiFi interface and or location.
The change advised to you by PlusNet predominantly impacts the line's error rate - with the higher SNRM though the synch rate will be slower, it is possible that with the consequential lower error rate, the effective data speed might be improved.
However for that to be the case in what you have being experiencing, one would have to believe that whilst running speed tests from the PC there were fewer line errors and when on the laptop there were more line errors.  I do believe that the change has made your line more stable (check the error rates) but I do not believe it is a cure for the problem as described.
Please though do keep us advised on how things progress.
Kind regards,
Kevin