Writer’s drawn on amendment to legal document (5,7)
I believe the answer is:
rider haggard
'writer's' is the definition.
(I've seen this before)
'drawn on amendment to legal document' is the wordplay.
I cannot really understand how this works, but
'drawn' could be 'haggard' (synonyms) and 'haggard' is located in the answer.
'amendment' could be 'rider' (amendment to a contract) and 'rider' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rider haggard that I've seen before include "English novelist" , "King Solomon's Mines author" , "Writer" .)
