Government office in tiny street beside railway (8)
I believe the answer is:
ministry
'government office' is the definition.
(term for a government department)
'tiny street beside railway' is the wordplay.
'tiny' becomes 'mini'.
'street' becomes 'st' (abbreviation).
'beside' is a charade indicator (letters next to each other) (I've seen this in other clues).
'railway' becomes 'ry' (abbreviation for railway).
'mini'+'st'+'ry'='MINISTRY'
'in' is the link.
(Other definitions for ministry that I've seen before include "church" , "Government department" , "Priests' work" , "a cleric has entered" , "Priesthood" .)