Had the tenner changed immediately (5,3,4)
I believe the answer is:
there and then
'immediately' is the definition.
(I've seen this before)
'had the tenner changed' is the wordplay.
'changed' is an anagram indicator.
'had'+'the'+'tenner'='hadthetenner'
'hadthetenner' is an anagram of 'THERE AND THEN'.
(Other definitions for there and then that I've seen before include "straight away" , "Instantly (but not here and now!)" , "Forthwith, immediately" , "Without hesitation" .)