Someone following in Model T, so parked up (7)
I believe the answer is:
apostle
'someone following' is the definition.
(apostle can mean a follower)
'in model t so parked up' is the wordplay.
'in' indicates the answer is hidden within the clue.
'up' is a reversal indicator (in down clue: letters go upwards).
'eltsopa' is hidden in the letters of 'model t so parked'.
'eltsopa' written backwards gives 'APOSTLE'.
(Other definitions for apostle that I've seen before include "John, perhaps" , "To lapse (anag) - ardent supporter of a cause" , "Missionary or evangelist" , "Vigorous supporter" , "Good man" .)