Unidentified Known Traffic?

[The Fat Controller]

This is the actual paragraph from the UK MATS Part 1.

[B]5.1 Unidentified Known Traffic
Separation minima are detailed in Section 1, Chapter 3.

In addition, separation may be deemed to exist between aircraft under Radar Control or receiving Radar Advisory Service and unidentified known traffic in the following circumstances:

a) When authorised procedures are in operation whereby the known traffic is under the control of another controller, who is utilising an ATS surveillance
system, and separation can be maintained by direct co-ordination;

or

b) When authorised procedures are in operation whereby track or vertical separation is deemed to exist.

I think the original poster was referring to situation (b)

This covers radar corridors and buffer zones etc, as in the scenario I quoted in my first reply.