For Todd and others who may have an interest, Testament are planning to release a 3-CD set comprising the entire 1960 M10 lecture/performance broadcast by Cooke, plus the 1964 world premiere of Cooke's M10, given by the LSO in Royal Albert Hall.
Cover in preparation
SBT3 1457 (3 CDs)
Berthold Goldschmidt
CD 1 & CD 2 Mahler: Symphony No.10
The realization of the completion of the Symphony with Deryck Cooke at the piano
Recorded at the BBC's Maida Vale Studios, 1960
Philharmonia Orchestra
CD 3 Mahler: Symphony No.10
World premier performance recorded live at the Royal Albert Hall, 6 August 1964
London Symphony Orchestra
Previously unpublished
I don't know what Testament's source is but I assume it's better than the air-check that's circulated privately for years. I was hoping BBC Legends would release this since they retain the original tapes, but presumably they've licensed them to Testament for this project.
James