Conservative fool stopped by European lawsuits (5)
I believe the answer is:
cases
'lawsuits' is the definition.
('case' can be a synonym of 'lawsuit')
'conservative fool stopped by european' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'fool' becomes 'ass' (both can mean a stupid person).
'stopped by' means one lot of letters goes inside another (I've seen this in other clues).
'european' becomes 'E' (abbreviation e.g. EU).
'ass' placed around 'e' is 'ases'.
'c'+'ases'='CASES'
(Other definitions for cases that I've seen before include "Clothes containers or court trials" , "Bags" , "Keeps a close eye on" , "Lawsuits or travelling containers" , "Instances; containers" .)