I think the true picture is that the cost of keeping the F3 in service until Typhoon is ready to fully replace it is minimal and most of it is already spent. I understand that is certainly not the case with Harrier and that running it down earlier will save £1bn.
Perhaps, Yeoman_dai, you could enlighten us with your plan to fill the gap in air defence that your suggestion would result in?
Better to have a fighter struggling for altitude than not to have a fighter at all.