Make old boy fib about government head (6)
I believe the answer is:
oblige
'make' is the definition.
(I've seen this before)
'old boy fib about government head' is the wordplay.
'old boy' becomes 'ob'.
'fib' becomes 'lie' (I've seen this before).
'about' indicates putting letters inside.
'head' indicates taking the first letters.
The first letter of 'government' is 'g'.
'lie' placed around 'g' is 'lige'.
'ob'+'lige'='OBLIGE'
(Other definitions for oblige that I've seen before include "press!" , "Morally influence" , "Do something as a favour to (someone)" , "Hold in debt" , "Constrain" .)