Illegal act on a European peninsula (6)
I believe the answer is:
crimea
'european peninsula' is the definition.
(I've seen this before)
'illegal act on a' is the wordplay.
'illegal act' becomes 'crime' (I've seen this before).
'on' means one lot of letters go next to another.
'crime'+'a'='CRIMEA'
(Other definitions for crimea that I've seen before include "Yalta peninsula" , "Scene of the charge of the Light Brigade" , "Ukrainian peninsula, site of a 19th century war" , "Ukraine peninsula, scene of war (1853-6)" , "Peninsula, scene of war 1853-56" .)