Joc your problem is almost certainly related to routing with sprintlink.
I have suffered being routed through sprintlink in the past and it was not pretty.
From memory somebody generally referred to as the Skuzzmeister (may or may not)
in the past mentioned that they are known for overselling there bandwidth. Also providing asynchronous routing where your incoming ping may take a completely different path on return, ie you may get a 100ms ping 1 way and 200ms the other.
If any of the above can be proven to be false, then i was probably drunk and will delete it in a heartbeat
I play on broadband from the UK with Nildram, not the cheapest by any means but good.
At one time they changed their routing and Sprintlink was the norm.
I politely explained the problems to Nildram and they very kindly changed the routing to avoid sprintlink.
I somehow doubt you will get BT to take any notice whatsoever.
Ok so this is a pingplot of my routing to AH.
You will notice it only takes 13 hops if you ignore the first which is my router, compared to your 16 and the pingtime is 115ms. Much better than your 139ms.
Flossy would be interested to see a pingplot of Zen connecting to AH.