Take legal possession of one thousand quid (7)
I believe the answer is:
impound
'take legal possession of' is the definition.
(I've seen this before)
'one thousand quid' is the wordplay.
'one thousand' becomes 'im' (I've seen this in other clues).
'quid' becomes 'pound' ('pound' can be a synonym of 'quid').
'im'+'pound'='IMPOUND'
(Other definitions for impound that I've seen before include "Take property into legal custody" , "Seize goods for an infringement of the law" , "Seize and take custody of (items)" , "Confiscate" , "Shut up" .)