A three-CD set of the Tertiary Phase was released in mid-October 2004, before the final episodes were broadcast. These CDs contain extended material, previously cut to make 27-minute episodes for radio. A two-CD set of the Quandary Phase was released at the end of May 2005, and a two-CD set of the Quintessential Phase was released at the end of June 2005. Both sets again include material that was originally cut for reasons of timing. The sixth series is scheduled for release on CD on 13 April 2018.