Tory backing socialist is deliberate (8)
I believe the answer is:
consider
'deliberate' is the definition.
('consider' can be a synonym of 'deliberate')
'tory backing socialist is' is the wordplay.
'tory' becomes 'con' (abbreviation for Conservative).
'backing' says the letters should be written in reverse.
'socialist' becomes 'red' (red is a kind of socialist).
'red'+'is'='redis'
'redis' in reverse letter order is 'sider'.
'con'+'sider'='CONSIDER'
(Other definitions for consider that I've seen before include "Reckon, deem" , "Deem to be, believe" , "Look at someone or something thoughtfully" , "Hold" , "Muse, mull over" .)