When a criminal court and a courtmartial have each jurisdiction in respect of an offence, it shall be in the discretion of¹ [the Chief of the Air Staff], the officer commanding any group, wing or station in which the accused prisoner is serving of such other officer as may be prescribed to decide before which court the proceedings shall be instituted, and, if that officer decides that they should be instituted before a court-martial, to direct that the accused person shall be detained in Air force custody.