Advances by bus up to central Neasden (4)
I believe the answer is:
subs
'advances' is the definition.
(short for subscription payments)
'bus up to central neasden' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'to central' says to take the centre.
The centre of 'neasden' is 's'.
'bus' written backwards gives 'sub'.
'sub'+'s'='SUBS'
'by' acts as a link.
(Other definitions for subs that I've seen before include "Advance payments" , "vehicles" , "Players in reserve" , "Club members' payments" , "Reserves at football (sl.)" .)