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A bit out of date, but this interactive map of step free London is very good
All the London railway stations :
Acton Central is on the London Overground network. It is suggested that the station is accessible via ramps of moderate gradient from street to platform. It is necessary to exit the station to cross platforms if in a wheelchair. There are also train boarding ramps available on request. See pictures and further accessible transport detail from links below.
Overground line : London Overground (North London line)
AccessAble Access Guide :
Accessibility friendly : Acton Central is a partially accessible train station. The ramps are of a moderate gradient. A subway links the platforms which has at least 21 steps.
General description : See wiki
More comment : National Rail Map & Guide, Platforms are accessible from the street via ramps. Exit of the station is necessary to change platforms via a step-free route.