Joan Greenwood and the London Lisp.
Joan Greenwood was 26 when she played the part of Sybella in KIND HEARTS AND CORONETS. I have long been fascinated to know the origin of the so-called 'London Lisp' which she occasionally uses within the film. Many, many years ago I heard a partial explanation of this lisping phenomena - as I understand it, it was a late Victorian/Edwardian Upper-Class mode of speech intended to distinguish such children from their inferior suburban peers. In later life these children may have employed it to attract the attention of others of the opposite sex for whatever purpose. Sybella certainly knew how to employ it to advantage.
My question is: does anybody have better information as to its origins and how it came about? Could it, for example, have been a French Governess import that the privileged children picked up? I'm speculating.
I tried without success to Google the term and found only a computer language listed. If anyone has sound information on this linguistic quirk, I would be very interested to hear it. Idle speculators are NOT welcome.