Yes, if the telephone worked it will have ruled that possibility out, but only if it's plugged into the same extension.

I'm just struggling to see how else attenuation could have been so high as it would appear the test had been carried out on the master socket and not the test socket. (I've seen high attenuation caused because of lack of microfilters as some phones offer at least some impedance at ADSL frequencies - at least until it's answered).

Possible a wire off to the particular extension used.

Not relevant now that the actual problem is sorted, however in response to a couple of points you have raised:

31.5/63.5 attenuation figures. Those are often the maximum the router will display and the actual figures can be a lot higher which would have been the case here if there were not wiring issues.

Even being a direct 485m it is possible to get that sort of attenuation. I have friends who are around 700-800m from the exchange with an actual line length of around 9km and others close to them are touching 10km

Which is exactly what I said...

In your first post I missed the "extension" .

If this is an old IPStream Max connection which good stats suggest, then IP Profile should rise on its in within a day, but might take up to five days

My nephew messaged me this morning saying his downstream profile is now
7.15Mbps and unsurprisingly he's seen a massive improvement
Cheers for the input guys.