Divert public besieged by soldiers twice (7)
I believe the answer is:
reroute
'divert' is the definition.
(I've seen this in another clue)
'public besieged by soldiers twice' is the wordplay.
'public' becomes 'out' (out can mean released to the public).
'besieged by' is an insertion indicator (inserted letters are surrounded or besieged).
'soldiers' becomes 're' (Royal Engineers).
'twice' indicates the doubling of some letters.
're' duplicated is 'rere'.
'out' placed into 'rere' is 'REROUTE'.
(Other definitions for reroute that I've seen before include "Send a different way" , "Send elsewhere" , "Send another way" , "Change directions" , "Send on different path" .)