Former taxi firm worker possibly in high spirits (9)
I believe the answer is:
exuberant
'in high spirits' is the definition.
(I've seen this before)
'former taxi firm worker' is the wordplay.
'former' becomes 'ex'.
'taxi firm' becomes 'uber'.
'worker' becomes 'ant' (worker is a type of ant).
'ex'+'uber'+'ant'='EXUBERANT'
'possibly' is the link.
(Other definitions for exuberant that I've seen before include "Full of beans" , "Lively, cheerful" , "Joyously unrestrained" , "full of glee" , "Full of energy, high spirits" .)