You are not giving me much to go on.
If an hostile aircraft was to be sanctioned for overflight then it would need one of two senarios.
1. It needed to have been issued with a MLS aircraft movement descriptor by Fighter Command Movement Liaison Section at least 12 hrs before the flight giving a timescale, take off point and landing point which corresponded to the flight track that would be used.
This meant that although detected and plotted the Filter Controllers would not know it was enemy and so not be designated as hostile.
However any deviation from typical and expected track/flying methods would cause anyone from the Filter Room Controllers to Group Ops to instigate an interception.
2. Filter Room Controllers and all controllers in the loop above to be ordered to class hostile as friendly.
An event such as this would be so strange as to cause talk and concern as to every one who could see the plot and the lack of interception attempt.
All the above would need to be mirrored in every Filter Room/Group Ops area that the overflight flew through.
Ross