"Mizter T" wrote

in
another part of the building there is a 'tunnel' where you can see the
remnants of the old ticket windows that seemingly provided for the
District line plus the few mainline passenger trains that actually
served Olympia.

Those ticket windows were operated by London Transport - though in the early
1960s on non-exhibition days the only passenger trains were the two
unadvertised departures to Clapham Junction. What is more, if you asked for
a ticket to Clapham Junction they would actually issue a London Transport
ticket to Elephant & Castle. By 1967 the Clapham Junction trains were
advertised, and were the last steam-hauled passenger service entirely within
Greater London.

peter