PM to ring Kabul warlord perhaps forsaking force (9)
I believe the answer is:
callaghan
'pm' is the definition.
(I've seen this before)
'ring kabul warlord perhaps forsaking force' is the wordplay.
'ring' becomes 'call' ('call' can be a synonym of 'ring').
'kabul warlord perhaps' becomes 'afghan'.
'forsaking' indicates named letters should be taken away.
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'afghan' with 'f' taken out is 'aghan'.
'call'+'aghan'='CALLAGHAN'
'to' acts as a link.
(Other definitions for callaghan that I've seen before include "Former prime minister" , "Former PM" , "3's Labour predecessor" .)