One Music is the radio show that replaced the legendry John Peel shows after his death in 2004. It showcases a wide range of new and unsigned music. There are three shows each week, each with a difference presenter with a difference emphasis in genre.
Tuesdays show is presented by Huw Stephens and has an emphasis on rock/indie.
Wednesdays show is presented by Ras Kwame and has an emphasis on UK urban music (hip-hop, dubstep, drum & bass, etc).
Rob da Bank
Thursdays show is presented by Rob da Bank and has an emphasis on electronic and experimental music.
One Music website
The One Music website has lots of information and advice about making music, and has MP3s from unsigned bands to download: