All the London railway stations :
Underground lines : Metropolitan, National Rail Chiltern Railways
AccessAble Access Guide :
Accessibility friendly : There is step free access between the street and Platform 2 for Southbound Metropolitan Line and National Rail services only. Customers need to be aware that there is a step between train and platform of up to 300mm for London Underground services. Boarding ramps are not available at this station.
Level access between street and platform southbound only, towards Harrow-on-the-Hill. The northbound platform is not accessible to wheelchair users due to stairs between the platform and street level.
General description : See wiki
More comment : National Rail Map and guide