For many years Episode 3 of the serial existed in the BBC Archives only as a black-and-white 16mm telerecording, as the 625-line colour PAL transmission master videotape for that episode was wiped for reuse by the BBC in 1976. Episode 3 was restored to full colour in 2008, using a combination of computer colourisation by Legend Films with software developed by the Colour Recovery Working Group. This version was released on DVD in 2009. The colour masters for the other five episodes are still extant.