French towns seizing queen while backing palace (10)
I believe the answer is:
versailles
'palace' is the definition.
(I know that Versailles is a palace)
'french towns seizing queen while backing' is the wordplay.
'french towns' becomes 'villes' (I've seen this in another clue).
'seizing' indicates putting letters inside.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'while' becomes 'as' (eg 'while I walked' means 'as I walked').
'backing' says the letters should be written in reverse.
'as' back-to-front is 'sa'.
'er'+'sa'='ersa'
'villes' placed around 'ersa' is 'VERSAILLES'.
(Other definitions for versailles that I've seen before include "Palace built by Louis XIV" , "Louis XIV's palace; WW one treaty" , "Palace near Paris" , "French palace" , "Royal Court" .)