The Belle Epoque styling in this advert is superb, from the hair and accessories through to the gloriously curvaceous model. Janet Reger adverts were always in a league of their own, and I think this may possibly be one of the Brian Duffy ones.
Scanned from Vogue, December 1977.
Liz Eggleston 
I loved Janet Reger lingerie. It was so glamorous. Sadly for a curvier figure than mine was in the 1970s. Memorable for me because while I was inside her Beachamp Street boutique in about 1975, I left my husband outside with my daughter in her pushchair. Along strolled Caroline Kennedy (daughter of) who was a student of my husband at Sothebys. She shook hands with my little daughter who has never remembered her brush with history.
Do we know the name of the model in the advert?