Leaders to allow lascivious Brits into French commune (4)
I believe the answer is:
albi
'french commune' is the definition.
(commune in southern France)
'leaders to allow lascivious brits into' is the wordplay.
'leaders to' says to take the initial letters (I've seen 'leader to' mean this (the letter which leads the word)).
The initial letters of 'allow lascivious brits into' is 'ALBI'.
(Other definitions for albi that I've seen before include "in south of France" , "French city, capital of the Tarn department" , "town in France" , "French town" .)