 In fact, the Doctor states that, whilst their behaviour is (on the surface) that of a military police force, they are really little more than "interplanetary thugs" for hire.They have no jurisdiction on Earth and no authority to deal with human crime (when hunting a fugitive alien in an Earth hospital, they transported the building to the Moon); they will, however, strictly obey any laws on the planet they are on (e.g.road speed limits).