Leader of Tories in posh headgear? Well I never! (5,4)
I believe the answer is:
fancy that
'well i never' is the definition.
(both are expressions of disbelief)
'leader of tories in posh headgear?' is the wordplay.
'leader of' says to take the initial letters.
'in' is an insertion indicator.
'posh' becomes 'fancy'.
'headgear?' becomes 'hat' (hat is a kind of headgear).
The first letter of 'tories' is 't'.
'fancy'+'hat'='fancyhat'
't' placed within 'fancyhat' is 'FANCY THAT'.
(Other definitions for fancy that that I've seen before include "exclamation of surprise" , "goodness" , "Gosh" , "Well I'm blowed!" , "Imagine!" .)