This is a great thread if you read the whole thing.

Before I read it I was puzzled by what I thought was a mix of British and American terms. I thought "subway" was only American. But Michael pointed out that in England a subway can be part of a tube station, a subterranean passageway that you might very well pass through between the stair and the turnstile, so it fits in perfectly.

I like Bill's suggestion that the woman in the chorus is Casey's mother in a nursing home. The chorus lyrics make more sense that way, particularly the line "now that you've a family of your own."

The only problem with Bill's idea, to an American ear, is Casey's mother putting on new stockings to please him. But perhaps in England in 1960 stockings didn't have a sexual connotation? Perhaps she's always dressed in a bathrobe and slippers and socks, as are many nursing home residents, and on a previous visit he said something about her socks being old, maybe suggesting that he could buy her new ones.

If the stockings are the same thing that we think of in 2014 America (after years of seeing hosiery advertisements showing young women in sexy poses with their stockinged legs completely exposed) then the woman must be an old flame or a hooker, and the fact that her way of looking attractive to him is to wear new stockings is sad. But the whole tone of the song is melancholy, so it fits in well.

Other than that, the only thing that's mysterious is the word "chain," as several people have pointed out. The song doesn't give us any clue as to what "his chain" is, and if it's a metaphor it doesn't fit in very well. I would be inclined to regard it as an unfortunate re-write, and sing "his train" instead, as Al suggested.

Casey went up to London and visited someone, perhaps his mother, and now he's riding the tube back to Victoria station, and as he has a little time before his train and is saddened by the whole trip he stops for a drink. He hadn't seen her for a long time before that, so if he's decided not to make this trip again it should come as no surprise.

A few things not mentioned previously: Kristofferson was at Oxford between 1958 and 1960, and was stationed in Germany in the early 1960's. The song was on his first album, released in 1970. His son born in 1973 by Rita Coolidge was named Casey.