In fact there's a deliberately unallocated pot of around £8bn (from memory) and a whiteboard of candidate projects to use it. Ministers have been dropping increasingly heavy hints that the MPA issue is recognised and will be addressed in the SDSR. Hammond says technological advances have opened up new options for the mix of platforms, so it sounds to me like something based around a slack handful of manned airframes complemented by some UAVs doing whatever they are able to do could be on the cards. The treasury could always snaffle back the unallocated pot as savings of course but that would be sending a difficult signal about how fiscal rectitude is rewarded. Then again there's an election looming too. But those risks aside, the current trajectory suggests that some form of MPA will emerge from the SDSR.