Scrub allowed in Scottish river (6)
I believe the answer is:
delete
'scrub' is the definition.
(I've seen this before)
'allowed in scottish river' is the wordplay.
'allowed' becomes 'let' (to let is to allow or permit).
'in' means one lot of letters goes inside another.
'scottish river' becomes 'dee' (I've seen this before).
'let' inserted within 'dee' is 'DELETE'.
(Other definitions for delete that I've seen before include "Erase or destroy" , "Strikeout, remove" , "Eras" , "Scrub" , "Wipe out" .)