One of the more widely accepted notions is that a strategic defence review must always be led from a strategic perspective, the clue being in the name!
Decide what you want the armed forces to do, decide how you want to configure them and then provide the funds, in full.
The 1998 SDR was widely considered to be an excellent document but it was never funded properly. The end result was a load of aspirations and a seriously top heavy set of capabilities that have been seriously exposed when faced with changing circumstances. The MoD has lurched fron one short sighted decision to the other, adding massive bills for tommorrow all driven by expedience.
So whilst we might all agree that a strategy led FDR is the most sensibe option is it the best.
What if we started with a fixed long term budget and worked out what we could do within it?