I watched this series passionately when I was a kid, growing up on a council estate in a family of complete philistines. Top of the Pops was the main fare in our house.
Unfortunately, I'm not sure I ever managed to see them all, as I don't recall them being repeated, and I have since searched in vain for any repeat showings onTV or DVD/video recordings, so any leads in that direction would be very welcome.
I would say that the hidden melodies were deliciously crafted and consummately performed, much better in fact than Jo did his Chopin. I have a painfully slow and clumsy recording of him playing the oh-so-popular Polonaise in A flat!
However, I do have a cassette tape somewhere of a selection of hidden melodies, which I will try to search out, as another friend of mine is also interested in them, and she is too young to have ever seen the series.
As for the handiwork involved, I think it was a talent on the part of Jo Cooper for spotting the similarity between the components of a tune and its resemblance to classical tunes penned by famous authors. No time to go into detail here, but I think it's obvious that some of the sea shanties like Drunken Sailor are fairly easy to knock into shape à la Vaughan Williams or Benjamin Britten, whereas one of the others that he set in the style of Mozart came out in such a Mozartian guise that it was hard to remember it was actually only a popular tune, written much later.
When composing in the style of Chopin, and I did this for my music A-level many times, I think the obvious things are to emphasize thirds and sixths, alternatingly and then add in a nocturne-type bass (think D flat here) for starters. Then certain rhythms are typically his (though not exclusively, of course): polonaise, bolero, mazurka.
I could go on, but I'm sure there are others out there better qualified to do this.
Tim (amateur pianist, Chopin fan, motorcycle freak and general nerd)