It's one of the world's most iconic songs, and is still played on radio nearly every day. This version however, is not the radio version of Under Pressure, but an A Capella version stripped of most of its instruments and production elements.
It was writter in 1981 by David Bowie and Freddie Mercury when Bowie teamed up with Queen to record vocals for “Cool Cat”. Bowie then suggested he and Murcury write a new song from scratch. Mark Blake, the author of a Freddie Mercury biography 'Is This The Real Life: The Untold Story of Queen' reports that Bowie and Mercury began a 24 hour marathon of song-writing and produced Under Pressure.
This is it, without its bells and whistles. It's incredible!
Source: Superstar Magazine