Top judges flirt with one of Diana's entourage (7,5)
I believe the answer is:
supreme court
'top judges' is the definition.
(highest court of appeal in a country)
'flirt with one of diana's entourage' is the wordplay.
'flirt' becomes 'court' (to flirt with could be to woo or court).
'with' is a charade indicator (letters next to each other).
'one of diana's entourage' becomes 'Supreme' (as in Diana Ross & the Supremes).
'court' put after 'supreme' is 'SUPREME COURT'.
(Other definitions for supreme court that I've seen before include "Its judgment is final" , "High legal authority" , "Ultimate US legal panel" .)