It might be Northern have to review some of their recruitment plans. Below is a quote from Bob Crow regarding agreements reached by RMT with Northern Rail. Quoted from the "Northern Rail Strike" thread.
PTR&R Regarding Promotion
The company states that should an internal candidate achieve the recruitment criteria, as long as there is a vacancy, they will be appointed ahead of an external candidate to a role. Should there be more than one successful internal candidate, then the best scoring internal applicant shall be appointed, subject to any satisfactory assessments and medicals that are required for the role. Further, should two internal candidates score the same, then the senior candidate will be appointed. Further, a commitment was given that a feedback mechanism will be put in place to ensure all unsuccessful candidates have the option of receiving developmental guidance on why they did not reach the required standard for appointment to the role applied for.