packet loss on routers may just be some QOS or something coming into effect, as the router drops low priority traffic, so you need to ping further into the network or something like www.google.co.uk to prove there is a real issue.
Well, I wrote in my original post that I had pinged www.talktalk.co.uk,
with the described results.
So what you are saying is that the packet loss I saw when pinging the Gateway IP was merely due to it being considered low priority traffic by the router?
I would rather think that as the Gateway IP itself was already part of a different subnet, the pinging went via some other TT server, which caused the packet loss.
But I am no expert on this, so I may be wrong. For example, I do not really know what the connection between the ADSL port IP and the Gateway IP is.