You need to complete an ‘Authority and Entitlement Certificate’ which can be found at Annex A to JSP 752, chapter 6, section 6 if it’s for yourself, or at Annex B if it’s for immediate family members. You should submit this to your Commanding Officer at least 6 weeks in advance of the date when you will be travelling. If you are required to proceed on assignment at short notice, and an assignment order has not yet been received, the written approval of the assignment authority must be obtained in addition to the CO’s approval.
When you receive the authorised certificate back, it will including details as to the maximum amount you will be able to claim