In the example you stated,
Using a VOR and associated DME/TACAN station. Both aircraft must have reported established on radials at least 20° apart.
One aircraft inbound and the other outbound from the VOR station, [track separation is established], provided that the outbound aircraft is at least 20 miles OR the inbound at least 30 miles from the station.
There are other criteria for two a/c inbound or two a/c outbound. These, and conditions attached to the separation standards can be found in CAP 493,
Manual of Air Traffic Services (part 1), Section 1 Chapter 3.
VL