Landed property this writer originally secured in valley (7)
I believe the answer is:
demesne
'landed property' is the definition.
(I've seen this in another clue)
'writer originally secured in valley' is the wordplay.
'writer' becomes 'me' (where the crossword setter is 'Bartland').
'originally' indicates taking the first letters.
'in' indicates putting letters inside.
'valley' becomes 'dene' (I've seen this before).
The first letter of 'secured' is 's'.
'me'+'s'='mes'
'mes' inserted inside 'dene' is 'DEMESNE'.
'this' is the link.
(Other definitions for demesne that I've seen before include "Domain" , "Estate; sound like belittle" , "Landed property used by the owner - needs me (anag)" , "Large landed property" , "Land attached to manor" .)