Insulting scoundrel detaining Queen, a right-winger (10)
I believe the answer is:
derogatory
'insulting' is the definition.
(thesaurus)
'scoundrel detaining queen a right-winger' is the wordplay.
'scoundrel' becomes 'dog' (dog is a kind of scoundrel**).
'detaining' means one lot of letters goes inside another.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'right-winger' becomes 'tory' (Tory is an example).
'dog' going around 'er' is 'derog'.
'derog'+'a'+'tory'='DEROGATORY'
(Other definitions for derogatory that I've seen before include "Showing a disrespectful attitude" , "Disparaging" , "deliberately offensive" , "Insulting" .)