EMI listed 44 titles in their official site, but thanks to Mark Whitehead, I found more than 60 titles on Spotify. Composers features in this series include: Bartók (3 volumes), Berg, Britten, Debussy, Delius, Dukas, Dutilleux, Elgar, Enescu, Falla, Glazunov, Hartmann (2 volumes), Henze, Hindemith (2 volumes), Holst, Honegger, Ibert, Janácek, Khachaturian, Kodaly, Korngold, Ligeti, Lutoslawski, Messiaen, Milhaud, Nielsen (2 volumes), Orff, Pärt, Penderecki, Poulenc, Prokofiev (2 volumes), Rachmaninoff, Ravel, Respighi, Rodrigo, Roussel, Satie, Schoenberg, Schreker, Scriabin, Shostakovich (2 volumes), Sibelius, Stockhausen, Stravinsky, Suk, Szymanowski, Tavener, Tcherepnin, Tippett, Villa-Lobos, Walton, Weill, R.V. Williams, Xenakis, Zemlinsky (2 volumes).
Here's the Spotify playlist: EMI: 20th Century Classics (1785 tracks, total time: 152 hours) Ctrl (CMD)+G to browse in album view. Albums are sorted by composer names, as listed above.