Station filling with trains initially working (10)
I believe the answer is:
paddington
'station' is the definition.
(train station in London)
'filling with trains initially working' is the wordplay.
'filling' becomes 'padding' (padding is a kind of filling).
'with' says to put letters next to each other.
'initially' suggests taking the first letters.
'working' becomes 'on' (on can mean working or activated).
The first letter of 'trains' is 't'.
'padding'+'t'+'on'='PADDINGTON'
(Other definitions for paddington that I've seen before include "A figure child might want for Play" , "London rail terminus" , "London station - famous bear" .)