Also consider BA out of YVR. BA has had some great Business & First Class fares showing up lately. If you are interested in adding a MR to your IST trip BA has an F (A) YVR-LHR-CPT itinerary pricing at USD $5007 return. The fares out of SEA/SFO/LAX are $2400 more and $1500 less than the sales out of the US West Coast over the last 2 years. The itinerary generates 53,585 EQM. As a MVPG75K it also generates 123,246 RDM.
There is also BA J LHR-PDX return for USD $2450. Just throwing out some ideas.
James