Ryan Henry had high hopes, no doubt, for his new musical — until some devastating feedback, neatly typed and mailed, from a fellow theatremaker.

“I don’t mince words when I’m asked to assess a piece,” began the note under a simple, capitalised letterhead — “STEPHEN SONDHEIM”. The words were, indeed, as un-tenderised as one of Mrs Lovett’s grisly pies.

“Your intentions are good and the attempt noble, but you’ve ignored some basic dramaturgical rules,” the greatest composer-lyricist in music theatre history, who died in November at 91, wrote. Henry’s show had a “static quality”, his numbers had “little relationship between the music and the lyrics”, “lack variety” and “state and describe rather than dramatize”. Ouch.

The letter was bravely offered to the Instagram account @sondheimletters, which sprung up after Sondheim’s death. There are hundreds posted, a treasure trove for fans, revealing not only the man’s generosity but the standards he held his art to.

“Whatever you write next,” Sondheim wrote, “I suggest you make sure that the songs dramatize the story rather than illustrate it and that you pay more attention to varying the material and being more meticulous in the execution of the songs.”