Judi Dench in Cabaret!
From the video’s notes:
Yes, that Judi Dench…from the original London production of Cabaret in 1968…keep in mind, the character of Sally Bowles from the original stories was supposed to be woefully untalented (this was changed for the Liza Minnelli film version) and this particular song was not included in the film.
It’s amazing, because she comes out in wig and makeup and a really bad recording and you’d never know it was her until she makes an expression and her mannerisms are exactly the same.
Indeed, by the time she’s in the pixie cut, she basically stopped aging (see also As Time Goes By through James Bond):
Judi Dench joking on Morecambe & Wise 1978