That also goes for Micheldever (used to have side platforms, I believe, and later turned into an island), though I believe the route forces you directly into the subway (I might be wrong about this). Can't actually remember if the station buildings are still open.
Not sure about the present situation, but four or five years ago the station building was open until about 9.30 as a ticket office. When I used it you could exit the building onto the original platform and walk to the end of it to get to the subway. Looking at the building from the island platform I don't think any of the first floor is in use.
If I understand your remark about the subway correctly - yes, you have to use the subway to get to the island platform. The subway takes you right under the tracks from the station building on the west side over to the east, and as you come up the steps there you see the bricked-up continuation that must in the past have led to the east side (down) platform, now completely vanished.
Going back to the start of the thread and the missing platform 7 at London Bridge, in the 1950s it was platform 5 that was missing. 1, 2 and 3 were platforms for Kent. 4, 6 and 7 were for Cannon Street and Charing Cross. There was a through track between the tracks for platforms 4 and 6, which I never saw being used, which was presumably the line that counted as "platform 5".