For staff expenditure, the following shall constitute supporting documents: ... (d) in respect of mission expenses: - the travel order duly signed by the competent authority, - the 'statement of mission expenses' showing, in particular, the place of mission, the dates and times of departure and arrival at the place of mission, travel expenses, subsistence expenses, and other expenses duly authorized on production of supporting documents; this statement shall be signed by the official on mission and by the administrative superior to whom the appropriate powers have been delegated.