If the pupil is FSM and then the parent joins the services due to FSM protection they will be recorded as both.
If the parents are separated and the child lives with the parent in the services they can be recorded as a service child.
If the other parent has parental responsibilities they can claim for FSM (to claim FSM the child does not have to live with the claiming parent) and therefore if awarded the pupil can be recorded as both.
If the parents are separated and the child lives with the parent who qualifies for FSM and not the parent who is in the services. The pupil must only be recorded as FSM and not a service child. However it could be the case they qualify for the service child pupil premium under the ever6 measure.
If the parent has left the services they can not be recorded as a service child but due to the service child ever 6 measure the pupil will still qualify for pupil premium.