United Imperial Constabulary
Over time, the Empire grew more prosperous and far-reaching. Enforcment of order by any single House, including the Imperial House itself, became unwieldy. Therefore, each House developed its own system of punishment and put in place the policing structure to implement this. In addition, to maintain order in matters which concerned more than one House (and so did not fall under the jurisdiction of said House’s own enforcement agency) but which did not warrant the direct attention of the Emperor himself, the United Imperial Constabulary were formed. Working for the Imperial house but not exclusively selected from it, the Constabulary liase with the security authorities in each of the five Houses. This has proven useful in order to keep the flow of information between Houses going and to note patterns in criminal activity which might not otherwise be spotted.
This primarily investigative body does not have the resources or manpower to challenge large physical threats to the Empire, which would be met with military force, combined from all Houses to form an Imperial Army. The UIC's impartiality in criminal matters helps to mediate between Houses where interests may be at odds and their discretion in such affairs is trusted by all. They normally work with a House's own police force when arresting suspects. Obviously only those who are truly honourable and highly skilled are selected for such a profession, and the pre-requisite training regime is known to be punishingly rigorous. It is also notable that their ranks contain several Imprint Psychics, an extremely useful skill in such work.
The Constabulary are, currently, primarily concerned with the petty but annoying pirate ships operating in the more remote sectors of several Houses outer territories. It is not yet certain where they may originate, but it seems that their activity is unrelated to ongoing rumours of underground organisations based within the Empire.
N.B. While PCs cannot play members of the UIC at game start, each House has its own military and policing force for those wishing to play investigators and police/security professionals.