He has a line on one (3)
I believe the answer is:
ian
'he' is the definition.
'a line on one' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
No letters remain.
This explanation may well be incorrect...
'has' acts as a link.
Can you help me to learn more?
(Other definitions for ian that I've seen before include "- Fleming (James Bond)" , "Albert Beale's first name in EastEnders" , "Boy's name (Scottish?)" , "... Fleming, author of the Bond books" , "Scottish John" .)