In Lambeth I calculated it to be morally correct (7)
I believe the answer is:
ethical
'be morally correct' is the definition.
(I've seen this before)
'in lambeth i calculated it' is the wordplay.
'in' says the answer is hidden in the clue.
'ETHICAL' is hidden in the letters of 'lambeth i calculated it'.
'to' acts as a link.
(Other definitions for ethical that I've seen before include "Conforming to accepted standards of behaviour" , "Moral, honest" , "Moral, principled" , "Relating to morals" , "Morally correct, in accordance with principles" .)