So, a week on: We're still getting occasional disconnections, but mostly come back at full speed. The difference now is - I can live with occasional disconnections, as long as the speeds (and connection) are stable when connected.
Disconnection today and it reconnected at 800Kbps upload, rebooted the router and it came back to near full speed.
Saturday was an issue where my parents stated the internet was more or less unusable. (Although there was apparently an engineer up the pole again Friday/Saturday). Unfortunately I wasn't here to check, and when I came back on Sunday morning (3am) the router had been connected for 18 hours at full speed.
These are the current stats
Data rate:9.465 Mbps / 55 Mbps
Maximum data rate:10.101 Mbps / 62.522 Mbps
Noise margin:3.9 / 7.6
Line attenuation:8.6 / 18.0
Signal attenuation:8.6 / 23.1
I will get that commend form done, all of the engineers have been wonderful chaps, and I don't blame any one of them for potentially not fixing the issue, it really is finding a needle in a haystack!
Edit:
I spoke too soon...
DSL uptime:0 days,00 Hours00 Mins06 Secs
Data rate:2.095 Mbps / 55 Mbps
Maximum data rate:2.095 Mbps / 59.503 Mbps
Noise margin:7.2 / 6.8
Line attenuation:8.5 / 18.0
Signal attenuation:6.8 / 23.1
It's definitely still not happy... Is there a preferred router that can give much more detailed stats? I did try putting OpenWRT onto our old Home Hub 5A, but I fried it in the process
(I think it had a bad NAND as it wouldn't successfully flash)
1 hour later it disconnects again, reconnected at full speed...
DSL uptime:0 days,00 Hours00 Mins17 Secs
Data rate:9.997 Mbps / 55 Mbps
Maximum data rate:13.824 Mbps / 62.870 Mbps
Noise margin:2.1 / 7.8
Line attenuation:8.4 / 17.8
Signal attenuation:8.4 / 22.8
It's really really REALLY not happy tonight - not 10 mins after it reconnected at full speed:
DSL uptime:0 days,00 Hours00 Mins02 Secs
Data rate:5.333 Mbps / 55 Mbps
Maximum data rate:5.333 Mbps / 60.804 Mbps
Noise margin:6.1 / 7.1
Line attenuation:8.8 / 18.2
Signal attenuation:8.8 / 23.3