Many thanks Pete for your time and nice explanation.

Below is the latest Graph Stats that confirms the problem on Easynet's side (samples to include set to 1000). First ISP is Viatel here (different gateway), but there is no problem up to hop 9, where first red appears. Also included hop 10 you was after - no problem there.
Hop 11, though, seems to be the culprit with quite heavy packet loss (5%). Hop 12 is Easynet's last router (in my original question incorrectly named as our server - ICMP was blocking at the time so that was the last possible hop).

My last question, Pete, would be:
Hop 12 doesn't seem to be affected from packet loss on hop 11 (high jitter, though), however, our server (hop 13) suffers from packet loss regardless. Would you still say hop 11 is to blame?

I can confirm that we get very similar graphs from all our remote offices in UK (last 3 hops constantly in red).

I really appreciate your help and all the best with next versions of your great tool.

David