All the London railway stations :
Finchley Road & Frognal is on the London overground rail
network, and is not accessible to wheelchair
travellers between street level and platforms.
Only ticket office has step-free access from street.
See pictures and further accessible transport in London detail from links below.
Underground lines : London Overground (North London line)
Accessibility friendly : No
General description : See wiki
More comment : National Rail Map & Guide