FIying LON->HND two weeks, outward N inward V, outward has no premium economy bid upgrade available. Is the only option to pay an eye watering £450+tax at the airport? There are still plenty of economy premium seats left on the plane...

"EMD number" starts 131xxx

edit: outward is JL42. It's also painful that it's £450 + tax when europe it's just 450 euro... would be cheaper to fly from paris...