Who actually shapes British defence procurement

Does the military propose procurement plans and simply leave government to choose what it will fund?

No; modern British procurement is a continuous negotiation in which military headquarters is only one part of a much larger civilian and departmental decision structure.

Procurement involves continuing negotiations across the Ministry of Defence before ministers choose what to fund. The displayed decision chart places military headquarters alongside several civilian and departmental functions. Military headquarters is described as representing about a quarter of those decision functions. That is a reading of the chart, rather than a count of every military voice in the process. Military personnel may be heard at other levels without holding the corresponding decision responsibility. A service requirement can therefore be altered before it reaches the funding stage.