Here Come The Huggetts 1948

It's an old British b/w film. About 18 minutes in Jack Warner goes upstairs to have a word with his niece/lodger, she invites him into her room even though she isn't dressed. In a scene that lasts about 30 seconds she's wearing a flared mini-fullslip. I'd say the slip is probably white adorned with lots of black lace, making for a deep hem and filing in the bust area, shoestring straps. IMDB has a still:

http://www.imdb.com/title/tt0040431/mediaviewer/rm1066686976

Possibly clearer here:
http://www.parkcircus.com/assets/0004/7699/ti104312_large.jpg?1341621127


Right near the end of the film Susan Shaw is sitting on the stairs showing some petticoat and talking about whether or not she needs to wear stockings;
http://www.imdb.com/title/tt0040431/mediaviewer/rm3734198784