Leopards from the Sea
Its entry in the Radiophonic Database has the notes:
Reel returned from Delia Derbyshire. TMS (Television Music Studio) tape dated 2/5/71 Sound Supervisor Adrian Stocks T/G Operator Ray Williams Box marked "Reel 1 of 2", title "Leopards from the Sea". Idented orchestral recordings.
Its tape's catalogue entry is dated December 1970, so the 2nd May 1971 might be the episode's broadcast date. Unfortunately, the records of Chronicle episode titles for 1971 are very partial and do not include this episode.