Search london history from Roman times to modern day
A bit out of date, but this interactive map of step free London is very good
All the London railway stations :
Underground lines : Metropolitan, National Rail Chiltern Railways
AccessAble Access Guide :
Accessibility friendly : Flat access to both platforms. BUT, to cross platforms there is a bridge which has in excess of 22 steps. There may be a way to access platforms by exiting the station.
General description : See wiki
More comment : National Rail Map and guide