“When Delia died, her partner Clive discovered all these boxes in her attic, just numbers of tea chests and cardboard boxes all falling to bits, all full of tapes which one day had sticky labels on them but all the sticky labels had fallen off and were at the bottom of the boxes so we were just left with hundreds of reels of tapes and the labels, so it was a real jigsaw puzzle.
Initially Brian Hodgson took delivery of the tapes [...] and he weeded out a lot of stuff because, basically, Delia seemed to have, when she left the BBC, just emptied her studio into the back of a car so a lot of them were either blank tapes or just echo tapes and just bits of edits which weren't going anywhere or duplicates of things we already had. So Brian did an initial sort of weed through but I still ended up with about 300 reels of tapes.” 
“When Derbyshire left the BBC in 1973, she emptied boxes of papers and tapes from her office into her car. They remained untouched in her attic. ... Following her death, Brian Hodgson suggested to Clive Blackburn, Derbyshire's partner, that Ayres be appointed to catalogue the almost 300 tapes.
Ayres returned to the Radiophonic Workshop Archive anything that belonged to it. However, that was just the beginning of a long, unfinished process. The problem was two-fold. On any one tape, there were pieces from separate, and usually different projects. Secondly, the tapes were improperly stored, and the sticky labels fell off. So any one box could have 30 tapes and hundreds of labels in the bottom of the box. There were nearly 300 tapes and the cataloguing alone would take at least six months.”
They were almost all digitized by Louis Niebur of the University of Nevada and David Butler in the summer of 2007 by playing them on a 1960s Studer A80 tape machine lent by the BBC's Manchester studios.
They contain the audio for dozens of pieces of Delia's music that were believed lost, including at least one Macbeth, the medleys she made for the ICI Fashion Show and the Brighton Festival, Le Pont Mirabeau, for Hamlet, Medea and Raven and Dove, but in the years since they were digitized, nothing has been published.
In theory anyone should be able to listen to them at the John Rylands Library where "membership is open to all over the age of 18" and in early 2014 the University of Manchester was given money to buy equipment to make this possible.
Unfortunately, the library currently [Sept 2015] says "the Delia Derbyshire tapes are not available for consultation by members of the public. There is currently an ongoing project around the tapes and as such there is hope that they will be made accessible in the future."
Mark Ayres' Initial Catalogue of the tapes records the labels on them and gives a brief description of each and in the last minutes of the documentary Inside Out there is a brief screen shot of the wav files created from her tapes, in which the following filenames can be seen
|DD134||DD134 Medea first wo[rking] tape.wav|
|DD135||DD135 Marlene Dietrich.wav|
|DD144||DD144 Lion basic voice.wav|
|DD145||DD145 Brian's backgrounds.wav|
|DD148||DD148 One Under The Eight.wav|
|DD149||DD149 Methuselah 3.wav|
|DD151||DD151 Left Channel only.wav|
|DD152||DD152 Military band.wav|
|DD157||DD157 Hamlet reel 3.wav|
|DD158||DD158 Dublin Macbet[...]sup.wav|
|DD1[..]||DD1[...] first [...]|
The WikiDelia has a page for what is known about each tape: see the Category:Tape.
There are hundreds more tapes of unpublished Delian work at the BBC, listed here on page TRW.
- Mark Ayres speaking in the Sculptress of Sound BBC TV programme.
- Mark speaks again about the Attic Tapes in an interview made for These Hopeful Machines.
- Breege Brennan's thesis
- BBC article Lost tapes of the Dr Who composer, 18th July 2008
- Heard by Martin Guy during a personal visit to Manchester in 2010.
- Message from James Percival in the Delia Derbshire mailing list.
- Slide 11 of 2007 presentation The Delia Derbyshire Archive at Manchester University
- John Rylands Library: Using the Special Collections
- David Butler pre-DD Day 2014 interview on soundcloud.com: "We've recently got some funding which will actually enable us to set up listening posts at Deangate John Rylands Library so that will allow people to go into the library and actually listen to the tape archive. You can't overstate the importance of that in terms of accessibility.
Interviewer: So when do you think that's going to be available for public access?
Butler (laughing): "I don't know" is the answer but I'll certainly be pushing for it to be in place as soon as possible."
- Personal email from John Ryland's Special Collections staff, September 2015.