HORRENDOUS download speeds even to PN sites

[#1]

Thanks for the assist!
It's looking as though Thursday was an anomaly and we cannot explain the massive number of disconnects there, but the Saturday, Sunday and Monday ones are roughly in line with the times I was looking at the router config so are down to manually initiated reboots.
Having eliminated MTU and other services I can consistently get 89kbits/sec between BT and iPlayer but not even a tenth of that through the browser unless I shut BT and iPlayer down.
I've got just a browser open and things are behaving themselves a bit better, so I guess it could be that 135k profile that's causing the bottleneck (although it doesn't explain latency to some websites like mozilla and PN portal that I don't see when going to other sites).

[#2]

Incidentally Joanne,
You can't help but notice there's been a bit of a run on people who had a spate of disconnections last week who're now on stuck profiles that are barely better than dialup.
My line's been reasonably stable (if not speedy) for over 3 years and it looks like a spate of connection drops over a 6 hour period resulted in an internet connection that's "stable" but so slow that it's maxed out whenever you try to do anything clever like download a rich webpage.
If people try rebooting the router (a reasonable troubleshooting measure), I can see that might compound the problem unless your reporting tools are intelligent enough to consider the possibility that some reboots are intentional.
If a customer's updated you at 07:30 and 20:00 saying "I rebooted the router" and each update is preceded by an "outage" then isn't there any way to manually tell the system to ignore those disconnects in the context of the 72 hour stability counter?

[#3]

I would have thought that the the couple of BT outages experienced last week would not be recorded on PN graphs as this data is confined to logging on to the internet and not the connection to the exchange. So PN would only see the internet connection being lost at the start of the outage and regained when the outage has been fixed. Rebooting the router during the outage would not be seen be PN.

[#4]

@tstaddon,
In my experience I wouldn't say I've seen more issues than usual since the outage.
@itsme,
The connections do not show during an outage and any disconnections during the outage would indeed not be recorded.
Jojo

[#5]

Hi,
I got a phone call earlier today saying that "a large number of errors" is the most likely cause of the variable speed issue you have seen" however both the Visual RADIUS graph and my router logs are suggesting that this statement is only true if it's still counting the disconnects from last Thursday. Since Saturday you can count the *unexpected* drops on one hand. 
My router is now cheerfully telling me that there's been no data errors for over 3 days - but it does admit that the router disconnected and reconnected - briefly - around 7:15am this morning and also disconnected around the same time on Wednesday.
It would normally have something in the logs indicating if this is a result of a power loss or line drop, but hasn't done that for a couple of days.
If it drops again between 7am and 8am on Friday morning then I'd be inclined to say it's not likely to be a fault with the cabling or microfilters.  In either case one would expect the drops to be far more random. A fault in the router cannot be totally ruled out, but it's unlikely.
We do get odd things like the lights in the house all flickering when the street lights go on and off but I'm not aware of those brownouts affecting the broadband connection.