Guardian's German writer taking one in (as I do here) (12)
I believe the answer is:
parenthesise
'as i do here' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'guardian's german writer taking one' is the wordplay.
'guardian' becomes 'parent'.
'german writer' becomes 'hesse' (Hermann Hesse).
'taking' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'hesse' enclosing 'i' is 'hesise'.
'parent'+'hesise'='PARENTHESISE'
'in' is the link.
(Another definition for parenthesise that I've seen is " put in brackets".)