A bit like this leading Tory ... (7)
I believe the answer is:
soupcon
'a bit' is the definition.
'like this leading tory' is the wordplay.
'like this' becomes 'so'.
'leading' becomes 'up' ('up' can be similar in meaning to 'leading').
'tory' becomes 'con' (abbreviation for Conservative).
'so'+'up'+'con'='SOUPCON'
(Other definitions for soupcon that I've seen before include "A vary small quantity, just a trace - from France" , "Very tiny amount" , "Tiny quantity" , "Smidgen" , "Dash" .)