I looked it up. As scandalous as the potential union of Lady Sybil with the chauffeur, Mr. Branson, would be, it was possible. Once in a while, high-born ladies married their gentlemen servants, after all, one would know them better than an upper class man who one met at tea, was proposed to at dinner and married the next season. However, it goes without saying that if one did marry down in rank, it provided great amounts of gossip. If a lady married outside of her class, then she joined him, not the other way around. Lady Henrietta Wentworth had plans to marry her footman, John William Sturgeon in 1764. She planned to become simply Mrs. Sturgeon, give up her fancy clothes and move with him to Ireland to be with his family. Sound familiar, non?
The reality though was as Lady Mary expresses to Lady Sybil, "Oh darling, darling, don't be such a baby. This isn't fairyland. What did you think? You'd marry the chauffeur and we'd all come to tea?". Sybil would have to be prepared to give up everything: all money, family, status, everything she has and knows to marry a man. Can you blame her for stalling in her decision?
Thanks to E. S.
Turner for publishing What the Butler Saw: Two Hundred and Fifty Years of
the Servant Problem by Penguin Books, 1962, and for helping me expand my
knowledge of this area.