I first read about this in Ed Bott’s blog. The BBC site explains it this way:
Download all nine of Beethoven’s symphonies here the day after they are broadcast. All the symphonies are performed by BBC Philharmonic, conducted by Gianandrea Noseda.
The page has a listing of when the performances are and when the music is available for download. Check it out at http://www.bbc.co.uk/radio3/beethoven/downloads.shtml