Question: Here in America, I was taught in the mid-60s by disc jockeys playing the Petula Clark song that in the UK "subway" means a pedestrian tunnel beneath a street, not an urban rail transit system. But on today's rerun of "The Saint", an episode set in London, a character with a British accent says to Mr. Templar, "She committed suicide. She stepped off a subway platform right in front of a train." This episode is in color, meaning it was made around 1968-69. 

So can subway be used for the Tube as well?

Answer: 
The author of the Saint novels, while not being American did live in the states for most of the period that he was producing the books, so it is possible that the particular usage you have picked up bled into the author's vocabulary during that time.

Leslie Charteris was born in Singapore to a Chinese father and English mother. He was educated in the north of England and briefly at Cambridge before moving to the US where he spent most of the rest of his life, so his familiarity with the niceties of the usage in regard to the London underground may have been limited by lack of exposure.

Of course, the line may be attributable to a script writer rather than Charteris, but even within the UK at that time the distinction between 'Underground' and 'subway' was, to an extent, peculiar to the *London* Underground. [*Glasgow's* underground railway](https://en.wikipedia.org/wiki/Glasgow_Subway) (the world's third oldest) has included 'Subway' in its name at its inception and currently.
As a term **subway** applies to many passages that occur beneath ("sub") street-level. The Oxford English Dictionary lists three usages that all have the general sense of a tunnel *under* something else:

> 
> 1 a. Chiefly British. An underground tunnel providing access to sewers and other subterranean public utilities, or used to convey water and gas pipes, telegraph wires, etc.
> 
> 
> b. A tunnel (esp. a walkway) beneath a road, river, railway, etc., permitting easy movement from one side to the other. The usual term in North America is tunnel.
> 
> 
> 2 An underground railway. Cf. earlier sub-railway n. 2. The usual term for the underground railways in North America, and for that in Glasgow. Often applied to other similar railways in non-English speaking countries (see quot. 1960), although metro n.2 is also a common designation. Cf. tube n. 7b, underground n. 3.
> 
> 
> 

All three have notes for regional use. In North America, underground passages tend to be tunnels. In the UK, these passages are subways. Meanwhile, underground rail would be called *subway* in most of North America and Glasgow but have specific terms in other places (the London Underground or Tube, the DC Metro, and so on).

It would be unusual to call London's underground rail a *subway* except by analogy. That said, it's possible that person using the tube was from [Glasgow](http://www.spt.co.uk/subway/), that they associated the platform with the underground walkways connecting platforms (of which there are many!) rather than the train platform, or something else semantically consistent but odd usage-wise.