I know the term 'positive radar control' from my contacts with US controllers and the FAA.
IMHO 'Positive radar control' dates back from the time when ATC changed from the mere provision of information to radar based control, with controllers providing 'positive' instructions such as headings, climbs and descents.
The flying community, used to a much higher degree of freedom when ATC was limited to providing information, needed to be convinced that ATC directives should be adhered to. That is how the tautological term 'positive radar control' was colloquially introduced to reinforce the new status of the controller.
Taking the tautology for granted I have always liked the term as it very well reflects the work of the controller, who is not the passive provider of information but the pivotal player in aviation preventing collisions.