Flakey Connection and Loss of Broadband Speed

[#1]

For the last few months, my broadband connection has been very flakey. Sometimes it'll be stable for 2, 3, 4 days then there'll be a period of a few hours or maybe a couple of days where the internet connection and then ADSL connection fails, reconnects after a minute or two, then drops again.
I can't relate these bad connectivity periods to any particular time of day or day of the week - seems to be fairly random. I get the impression, however, that it's slowly been getting worse.
For a long time (years) I've regularly got around 10 Mb download and 1 Mb upload; this has been true even with the recent flakey connection - when connected.
The last few days, when connected, the download speed has dropped to 5 Mb and the upload to 0.5 Mb.
The Data Transfer Speed page on the Plusnet website tells me:
Estimated line speed:
    11Mb (This may vary between 6.5Mb and 15Mb) - Checked on 2016-01-08 19:00:50
Current line speed:
    5.8 Mb
I'm not very familiar with all the issues of ADSL and broadband but I'm guessing the flakey connection, having slowly got worse, has resulted in Dynamic Line Management dropping the connection speed?
This suggests to me that the problem is not with my home cabling or modem/router but probably between the house and the exchange?
If so, how do I get this checked?
It might be related but there's a lot (800+ ) of new houses in my area, some quite close to my house. There are also regular OpenReach vans parked at the local cabinets with engineers poking away ...

[#2]

Quote

I'm not very familiar with all the issues of ADSL and broadband but I'm guessing the flakey connection, having slowly got worse, has resulted in Dynamic Line Management dropping the connection speed?

Yes, that definitely appears to have happened.

Quote

This suggests to me that the problem is not with my home cabling or modem/router but probably between the house and the exchange?

The only way to be certain of that is to try another known working router, we'd recommend that as the next step if you can and to connect that to the test socket: http://www.plus.net/support/broadband/master-socket-guide.shtml
One thing I notice straight away from your connection logs is that looks like you might be powering the router off overnight, if that is the case please refrain from doing so as it will cause DLM to assume there's a fault and lower the speeds:
If this continues to be a problem please report a fault with us over at http://faults.plus.net
<img src="http://community.plus.net/visualradius/generated/image14531968199004.png"/>

[#3]

Welcome to the forum -that doesnt look to clever
Do you leave your router on all the time?
Can you try a quiet line test - using a wired phone dial 17070  option2 and listen for crackles hissing humming. As the fault is not there all the time you should repeat the test
form time to time.