Surely agree bout fixed (2,5)
I believe the answer is:
no doubt
'surely' is the definition.
(I've seen this before)
'agree bout fixed' is the wordplay.
'agree' becomes 'nod' (I've seen this before).
'fixed' is an anagram indicator.
'bout' anagrammed gives 'oubt'.
'nod'+'oubt'='NO DOUBT'
(Other definitions for no doubt that I've seen before include "sign of agreement" , "Surely" , "Bound to, unquestionably" , "To be sure" , "Almost certainly" .)