SBW
The draft letters are in the ASPSI. The ASPSI is clear that the Desk Officer must get a written certificate from your prior to nomination. The final para reads
The revised policy will ensure that, except in cases where the Service need dictates that an individual who is not prepared to accept the RoS requirement must be trained, personnel will be committed to provide the required RoS. Personnel will be aware, from signing the acceptance certificate that this will bar them from premature exit from the Service until they have provided the required RoS.