Keep losing Internet

[#1]

I'm still a bit bothered by that first photo - there's more wires visible than you've accounted for.

[#2]

One used to go to sky but is not used, and one is an extension upstairs but is not used either.

[#3]

OK I've got the picture now - and I really don't like it. Even if it was working better before I'm pretty sure it wasn't giving optimal speeds.
Firstly the extension lead running to the other socket is not the best way to do things and then you have the other extension cable from the filter to the router upstairs. A far, far better arrangement would be to have the router by the first socket and run a CAT 5e ethernet cable upstairs (to an £5 to £10 ethernet switch if you need multiple connections upstairs).
I suggest you try plugging the router directly in to the first socket with all other sockets empty and compare the router stats (sync speed, attenuation and noise margin) with the current arrangement. That will confirm if an improvement can be made.

[#4]

I will have to try a different setup, not much can be done much differently and these are a lot shorter runs now than previously.  Have been with Plusnet since 2005 and have never had problems until now.
Took these reading off the router connected as it is -
Item                                  Downstream            Upstream        Unit
SNR Margin                    15                              23                    dB
Line Attenuation              26                              14                      dB
Data Rate                        7101                        448                    kbps
Never took any previous readings so I am not sure if this is better or worse than I was getting a few months back.  Seems to coincide with the switch to ADSL2+.  My Profile is at 8000 but fluctuates, have seen it at 7150, and 6000 last week.
Also attached a few btchecker results I have been taking over the last weeks