The MPS, like the RMP, are distinct from their civilian counterparts in HM Prison Service. Manned wholly by volunteer transfers from the Armed Services, their main task is to provide rehabilitation training within a secure environment for Service personnel who are either to be retained in the Service or be dismissed.

The manning of the detention companies within the Military Corrective Training Centre (MCTC) and the provision of military instruction to service personnel under sentence is their main role at home.

Outside MCTC they provide a custodial service to the Forces conducting mandatory inspections of Unit custody facilities, and investigate incidents in unit guardrooms, which relate to custody.

The MPS also provide the Unit Custody Staff Course (UCSC), which trains unit regimental police personnel in the operation of unit custody facilities.

Critically the MPS also provide operational support through the provision of advice on Prisoner of War handling through the Provost staffs. They provide the technical advice required to the PW Guard Force and monitor the PWs in custody. Like the RMP, the MPS operational role in Peace Support Operations (PSO) has historically sent them to deal with the myriad of custodial issues that affect host nations in the event of the collapse of Law and Order.

In recent history MPS have been responsible for the provision of custodial facilities for indigenous criminals and internees. In Iraq they were responsible for the regeneration of the Iraqi Custodial System. The MPS are deployed today providing technical custodial advice in Iraq to the Security Sector.