With wit, Mrs T seen off in Parliament (11)
I believe the answer is:
westminster
'parliament' is the definition.
(I've seen this before)
'with wit mrs t seen off' is the wordplay.
'with' says to put letters next to each other.
'off' is an anagram indicator.
'wit'+'mrs'+'t'='witmrst'
'witmrst' put next to 'seen' is 'witmrstseen'.
'witmrstseen' anagrammed gives 'WESTMINSTER'.
'in' is the link.
(Other definitions for westminster that I've seen before include "(Seat of) Parliament" , "Houses of Parliament borough" , "London borough - abbey - parliament" , "public school" , "London borough and cathedral" .)