@ Darren
I think its pretty obvious from your tracerts youve provided that yours is a routing problem between hop 3 and hop 4 which are both on the BT 21CN network which is causing the increased latency.
When it happened to me I had similar tracerts which mapped out the old and the new higher latency showing the increase time in the BTw core network.
My old (BTw based) ISP at the time did actually take it up to BTw on my behalf. iirc mine increased from 16ms to 28ms and despite a well known (now ex) CS rep taking it further up the heirarchy in BTw... he didnt get any joy as they seem to consider anything less than 30ms acceptible.
The suggestion to leave the router off really was just a vain hope.. because mine stuck for a few weeks several times and me trying a d/c didnt work. It would always occur after some planned works... and it would go back again after yet another PEW. Because its on the backhaul then its probably going to need a d/c from between the exchange MSAN and the RAS before it picks up any new routing.
I know once it went 'back to normal' after a planned lift and shift for some other unrelated issue. Off the top of my head I probably saw about 5 or 6 of these incidents during a 3 year period. I would get stuck with the longer routing anything from about a week to about 8 weeks.
Sorry I cant recall exact details because its quite a while ago and Im now LLU. But I can fully sympathise with you because Ive "been there" several times and its so annoying that you know full well its routing between the exchange and the RAS... you have the proof.. yet BTw still consider it acceptible.
I hate to say this, but I think you may just have to sit tight for a few weeks and hope that a PEW comes up soon.
(Sorry for the bad pun).