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A bit out of date, but this interactive map of step free London is very good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 :
Drayton Park is on ThamesLink, and is partially accessible to wheelchair users to access platforms. See pictures and further accessible transport in London detail from links below.
National Rail : ThamesLink
AccessAble Access Guide :
Accessibility friendly : Partial. The map suggests that you can cross from one platform to the other, although there are no ramps. There are 50 steps to enter or exit the platforms.
General description : See wiki
More comment : National Rail Guide & Maps