Required New England Democrat to interrupt fuel supply (7)
I believe the answer is:
needful
'required' is the definition.
(I know that required can be written as needful)
'new england democrat to interrupt fuel supply' is the wordplay.
'new' becomes 'n' (abbreviation as in New Testament NT).
'england' becomes 'E' (short for England).
'democrat' becomes 'd'.
'to interrupt' indicates putting letters inside.
'supply' indicates an anagram (in a supple way).
'fuel' is an anagram of 'eful'.
'd' placed within 'eful' is 'edful'.
'n'+'e'+'edful'='NEEDFUL'
(Other definitions for needful that I've seen before include "Requisite, necessary" , "Nude elf (anag.)" , "poor" , "Required" , "Indispensable" .)