The source for the leak is the BAFTA-winning actress Miriam Margolyes, whose movie credits include “Being Julia,” “Harry Potter and the Chamber of Secrets,” “Romeo + Juliet” and “The Age of Innocence.” Margolyes unsuccessfully auditioned for a role in the upcoming play.

Leigh’s first new stage play since 1993’s It’s a Great Big Shame! is still untitled (Leigh always develops characters and situations with his casts, only firming up the play towards the later stages of his 18-week process). It will open in the National Theatre’s Cottesloe on Sept. 15.

Reports the Jewish Chronicle: “One performer who didn’t make the [casting] cut was . . . Miriam Margolyes, who auditioned, unsuccessfully, for a part. Speaking from her Los Angeles home, she revealed only that the play “is about being Jewish.”

A small tidbit of information, but more than was expected to be leaked from Leigh’s ultra-secretive preparation process. The play’s participants, however, have been announced. It will be designed by Alison Chitty, with lighting by Paul Pyant, music by Gary Gershon and sound by John Leonard. The cast includes John Burgess, Ben Caplan, Allan Corduner, Adam Godley, Caroline Gruber, Nitzan Sharron, Samantha Spiro and Alexis Zegerman.

Leigh’s last film, “Vera Drake,” won the Golden Lion at the 2004 Venice Film Festival and bagged Imelda Staunton (its leading lady) a BAFTA, as well as Golden Globe and Oscar nominations.