LEGALLY? No, you just need to file the paperwork. They don't even really care about the ceremony details beyond there being an officiant and witnesses to sign the papers, and proof everyone's of legal age or has parental consent. I think the Anglican position, which is not that different from the Catholic, is it SHOULD be consummated and *refusal* to do so would be grounds for annulment. That's as in one partner actively refuses to have sex with their spouse. Though here, the issue is less that there was no actual sex (as clearly William couldn't provide it--heck, if Lavinia married Matthew as it currently stands, or rather he doesn't, they'd be in the same boat, just not with imminent death as an out) but that Daisy, in her own mind, entered the marriage under false pretenses. She didn't love William, she didn't want to marry him, she only went through with it under extreme duress with outside pressure. She actually only would need to say that she did not mean it, her vows weren't sincere, and it was never a true marriage in her mind. Even in Catholicism, let alone Anglicanism (where divorce is sort of permissible if strongly discouraged) that would be more than enough to declare the marriage having never existed. Basically she said there wasn't a marriage the minute she said she didn't mean it or think of it as a real marriage. As for Ethel and Major Mustache, whether it was once or a couple times, it was clearly casual sex on his part, no matter what she made up in her head.