This is what it says on the 'About' page:
Audio is available to play online as streaming
64kbps MP3s. We've chosen this format because using
lower quality audio reduces the costs of running the
prototype which means we can include more programmes
with the budget we have available.
For the time being you can only stream audio from
the website itself. This is because we're interested
in seeing how much of each programme you listen to
which we can't do with downloaded files. We may make
downloads and podcasts available in a later
iteration.