Surplus to requirements and that’s new! (6)
I believe the answer is:
unused
This clue might be a double definition.
'surplus' is the first definition.
(thesaurus)
'new' is the second definition.
('unused' can be similar in meaning to 'new')
'to requirements and that's' acts as a link.
This may not be correct. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for unused that I've seen before include "'Fresh, new (6)'" , "Unaccustomed" , "Surplus" , "Neither employed nor second-hand" , "In mint condition" .)