is a list of current MR transfer partners.
Of those, the obvious standout for DC-London travel is British Airways. However, BA adds fuel surcharges to award tickets. A ticket from IAD to LHR costs 40,000 miles plus $699.
Aeroplan (Air Canada) would get you on a United flight for 60,000 miles and $238. Lower fees, higher miles.
Now, we get into the weeds.
All Nippon has a difficult award search, but will get you from IAD to LHR for 43,000 miles and $55 on United. They don't collect a fuel surcharge for transatlantic flights, but if you head to Tokyo, they hit you for $660.
So, many options. ANA looks good, but you'll have to find availability on United, transfer the points from MR to ANA (can take up to 2 weeks) and then call ANA to book.
I'm sure some of the other programs can get you there as well. It may be worth it to search their award charts for the best redemption. I'm not as familiar with some of the other programs, so can't speak to them as well.
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