I do not know for row 22. But my recent experience is that it is difficult to get the "nose" seats (F seats of teh 747 sold as C seats on domestic flights) when you check-in in Europe. I was in F from CDG-BKK-HKT, but they could only gave me a C seat on the BKK-HKT at check-in (they tried hard). Too late to get it changed to a "nose" seat when I got in BKK lounge. But, I got a "nose" seat when I checked-in at HKT for my return trip. My guess is that they are unsure of the plane they will actually use at the time you depart LHR so do not allocate the "nose" seats until the plane is determined.