I have to follow source of Government grant (4)
I believe the answer is:
give
'grant' is the definition.
(synonyms)
'i have to follow source of government' is the wordplay.
'i have' becomes 'ive' (contraction of 'I have').
'to follow' means one lot of letters go next to another (some letters go after or follow others).
'source of' indicates taking the first letters (the start - or source - of the word).
The first letter of 'government' is 'g'.
'ive' after 'g' is 'GIVE'.
(Other definitions for give that I've seen before include "Supply; elasticity" , "Transfer possession" , "Award" , "6" , "Donate or hand over" .)