Recklessly determined he will be new Tory leader (4-4)
I believe the answer is:
hell-bent
'recklessly determined' is the definition.
(I've seen this before)
'he will be new tory leader' is the subsidiary indication.
'will' becomes 'll'.
'new' becomes 'n'.
'tory leader' becomes 't' (I've seen this in other clues).
'he'+'ll'+'be'+'n'+'t'='hellbent'
(Other definitions for hell-bent that I've seen before include "Dogged - persistent" , "Absolutely determined" , "Recklessly determined" , "Dead set" , "Determined at all costs" .)