Completely step-free stations

Roding Valley does have steps into the ticket hall iirc, although they are easily bypassable. It is not possible to cross between platforms other than via the street or the stepped footbridge.

Kew Gardens has a flight of about 4 or 5 steps from the street to the southbound/westbound platform with an adjacent ramp. The subway is step-free but the gradient is quite steep iirc. The footbridge has steps.

Woodside Park I think has completely step-free access (other than a kerb) from the street to the adjacent platforms but crossing between platforms requires using a stepped footbridge or circa half-mile walk via a road bridge.

High Barnet has two entrances. Both can be accessed step-free from the street, but the higher one is accessible from the platform only via the stepped footbridge. There are also several rooms off the platform that are not step-free (at least some are non-public, but I'm not certain that toilets and/or waiting room are not located here)

South Woodford is step-free from both adjacent streets, but the platforms are connected by a stepped footbridge and a public subway that has stepped and ramped access.

Woodford is similar but one of the entrances to the eastbound ticket hall is accessed by a single step.

Both platforms at Epping have step-free access to the street but the street entrance to what was the westbound platform when it was a through station is only open at peak times AIUI. The platforms are only connected by a stepped footbridge or nearby road bridge.

The Jubilee line platforms (13-15) and the Stratford International bound DLR platform (16) are completely step-free from the new Carpenters Estate entrance, but access to all other parts of the station requires lifts. The Canning Town-bound DLR platform (17) is the only one completely step-free from the main (Stratford Square/bus station) entrance. The high-level DLR platforms (4a and 4b), both westbound Central line platforms (3 and 3A) and the westbound Elizabeth line platform (5) are completely step free from the mezzanine entrance (although 3 and 5 use a ramp to bypass stairs), this entrance can be reached without stairs/lifts only via the bridge from Westfield. I think it is theoretically possible to use the two entrances to interchange step-free without lifts between the westbound Central line and Jubilee line, but this is a circuitous circa 1 mile walk via streets.

The platforms at Stanmore can be accessed via ramps (or stairs) from the car park but there are steps to the main entrance.

Both platforms at Buckhurst Hill are accessible via ramps from a public subway but the main entrance and ticket hall are accessed only via steps.

Both platforms at Sudbury town are accessible on the level from the street, and the combined public and station footbridge between them has both ramps and steps, although the entrance to the ramps is around 50 m from the station entrance on both sides.

Heathrow Terminal 4 is step free within the station, but I think a lift is required to access the station level from the terminal.

Hammersmith (H&C) has a stepped footbridge between the London (north/east) end of the platforms, but I don't think this is currently in public use (it used to be) making it step-free to all public areas

Chesham is completely step free to all public areas with the possible exception of the garden in the former platform track bed (it isn't step-free but I'm unsure if it's a public area).

Elm Park, Dagenham Heathway and Upney are all step-free from the street to the platform via relatively steep ramps and don't have any public areas that require steps to access AFAIK.

There are several other stations where one platform is accessible without lifts or stairs but the other isn't (e.g. Debden, Ruislip) and plenty where interchange can be made only on the level/with ramps. I think this is it though for the Underground.

On London Overground:
Enfield Town and Cheshunt have only level access/ramps between the street and platforms.

Anerley, Bush Hill Park, Penge West and South Acton have level access from the street to both platforms, but access between them is via a stepped footbridge or a road bridge (a long walk at Penge West and South Acton).

At Liverpool Street, the LO platforms are accessible via a shallow ramp from Broadgate Circle but I think all other entrances require lifts or stairs.

Emerson Park has no steps and is accessible only via a moderately steep ramp.

Acton Central has ramped access only to the Richmond-bound platform, the Stratford-bound platform is accessed by a choice of a ramp or a steps. Access between the platforms is via the road level crossing or stairs to the subway.

At West Croydon the LO platform and adjacent NR platform are connected by steps and ramps. Access to the ticket hall and southbound NR platform is via stairs or the car park and street.

Uxbridge

The ramp seems to be permanently closed at Romford with the new access arrangements.

Chalfont and Latimer have flat access both sides, but it's a 200+metre walk along the pavement and under the bridge if you're not being picked up by car. But there may be time restrictions for the rear entrance...

A few stations on the northern end of the Metropolitan Line are like that: Chorleywood, Chalfont and Latimer, Chesham, and maybe Rickmansworth too.

Croxley could easily have step free on the up platform: the locked gate to the car park has been there for decades (the peak hours ticket inspector's booth I think is still there, or not overly long removed), and could suffice with an Oyster reader and camera: I seem to frequently find the main gate line locked open, presumably for the human presence PNB (sorry, I don't know what their job title is). And down platform wheelchair users could continue to Watford, and back to Croxley for the car park gate. I gather this process is used elsewhere.

There is very little point in having step free access on the up platform if there isn't step free access/egress on the other platform.

I kind of see where you are coming from, but if car park to platform is judged to be part of step free station criteria, all those stations that have no car park at all are so debarred from being classed as step free since anyone could then argue to include the nearest public non-station car park - and in central-er zone-s at least there must be precious few such car parks, never mind those that do that are of step free.

I understand the specific issue at Croxley, and it no doubt applies at other locations, but really to count step free access from car parks as counting is going - excuse the pun - one step too far. Not saying no step free access from a car park to a station is unimportant, just that trying to include it in step free station is not right.

Walking past the Croxley car park entrance, as many others do, I would certainly use the car park route + gate. I know many wheelchair users, being involved with a Ricky Disabled sailing club, and with the exception of a few local users, all arrive in adapted cars/vans. And a facility even as suggested would suck in users from over a much larger area if the only one available.

Many of the ageing residents would appreciate lifts, but one has to be realistic with the budgeting problems. If there's a mum struggling up, I'll help, buggy preferably without child (especially visiting grandson)!

Technically this is under the step-free development thread, because right now they are conducting feasibility studies for step-free access there

hmm, that means I have a photo of a station subway (taken July 2013) labelled as Kew Gardens that's actually somewhere else. It's been a long time since I've needed to change platforms there, the last couple of occasions I've been there walked to/from other stations.