Former agency worker given golden handshake at the end, spontaneously (9)
I believe the answer is:
extempore
'spontaneously' is the definition.
(I know that spontaneously can be written as extempore)
'former agency worker given golden handshake at the end' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'agency worker' becomes 'temp' (temporary worker sent from an agency).
'given' says to put letters next to each other.
'golden' becomes 'or' ('or' is the name for gold in heraldry).
'at the end' suggests the final letters.
The last letter of 'handshake' is 'e'.
'ex'+'temp'+'or'+'e'='EXTEMPORE'
(Other definitions for extempore that I've seen before include "without warning" , "Impromptu, improvised" , "Ad lib" , "Without preparation, of a speech say" , "on spur of the moment" .)