Divert public besieged by soldiers twice (7)
I believe the answer is:
reroute
'divert' is the definition.
(I've seen this before)
'public besieged by soldiers twice' is the wordplay.
'public' becomes 'out' (out can mean released to the public).
'besieged by' indicates putting letters inside (inserted letters are surrounded or besieged).
'soldiers' becomes 're' (Royal Engineers).
'twice' shows that letters should be duplicated.
're' duplicated is 'rere'.
'out' inserted inside '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" .)