Hack pursuing dull old tax collector (7)
I believe the answer is:
matthew
'tax collector' is the definition.
(I know this)
'hack pursuing dull old' is the wordplay.
'hack' becomes 'hew' (I've seen this before).
'pursuing' means one lot of letters go next to another.
'dull old' becomes 'matt' (I can't explain this - if you can you should believe this answer much more).
'hew' put after 'matt' is 'MATTHEW'.
Can you help me to learn more?
(Other definitions for matthew that I've seen before include "Patron saint of tax collectors" , "- Arnold, English poet" , "Generally accepted author of the first Gospel" , "Religious author" , "Gospel-writer" .)