“Fornication” was not/is not a crime.
It certainly was at common law. It was illegal in WV until 2010 and illegal in VA until 2005 when the Supreme Court ruled that the law could not be applied because of Lawrence v. Texas Virginia Supreme Court Strikes Down Fornication Law | American Civil Liberties Union
That reminds me of the great Damon Runyon short story “Breach of Promise”. It’s set in 1930s New York, of course.
The report you link to suggests that fornication was a statutory offence in Virginia; there is no suggestion that it was ever an offence at common law.
I agree with DPRK. I practice in a common law jurisdiction. SFAIK fornication has never been a crime and we have no legislation decriminalising fornication.
But in any case the OP was about a specific British incidence. I don’t think fornication between unmarried people was ever a crime here, but even well into the nineteenth century could lead to various sorts of social humiliation, which could be as powerful. It was not unknown for the errant to have to make a public confession to their church parish and to perform some sort of ceremonial penance (important when the only form of social security was from your parish) - though this could also serve to pressure a man to marry, especially where a breach of promise case in the courts might be financially out of the question.
The plot to half of the “Jeeves & Bertie” short stories by PG Wodehouse is that he’s accidentally gotten engaged to some girl (through a misunderstanding), and now he needed to get her to break the engagement. He couldn’t just go break it himself for fear of a breach of contract lawsuit. A convoluted plot followed, usually the brainchild of Jeeves, to make her think that Bertie was not the man she thought he was.
Also, on the TV show The Duchess of Duke Street (set in the Edwardian era), one of her regular guests is sued for breach of contract under false pretenses (not a spoiler; the audience knows what’s going on). The “Duchess” testifies on his behalf, and basically the entire court case is dramatized. I don’t know how realistic is it, or if it’s based on an actual event-- the “Duchess” is based on a real person, Rosa Leyton, but loosely based, so this could be a made-up event, but these trials did happen.
Now that we’re collecting pop culture references to “breach of promise”, there is also a Monty Python sketch (included in the It’s a Living episode of the second series/season of Flying Circus) called “Marriage Registry Office” in which that action is referred to (“There is such a thing as breach of promise, sir!”). Can’t find it on Youtube, the hits I get are for “Marriage Guidance Counsellor”, which is a different sketch. The episode was recorded and aired in 1970.
Thanks to this thread’s revival, I’ve had the opportunity to learn of a pivotal breach-of-promise judgment upheld by the Kentucky Supreme Court in 1937 (semi-hilarious details here), as well as a squeaker of a decision by the same court in 1997 tossing out a similar case (the justices’ vote was 4-3 in favor of the defendant).
The bottom line seems to be the courts’ views that women are no longer helpless little flowers dependent on men, and thus breach-of-promise cases are an anachronism.
Don’t forget Bardell v. Pickwick in Dickens’s Pickwick Papers.
Well, not when it was Under the Consent of the King. In fact, there was a word coined to describe that policy. 
Utcotk? 
It is true as a broad generalisation that fornication was not a crime under English law. But it was an offence under ecclesiastical law and could be prosecuted in the church courts. Cases often involved allegations of premarital sex. Moreover, Parliament did make it a crime in 1650. That was a direct replacement for the ecclesiastical offence, prompted by the fact that the church courts had been abolished. Both the abolition of the church courts and the 1650 Act ceased apply at the Restoration. But it is a well-known fact of English social history that the church courts in England were increasingly ineffective in such matters after 1660.
And to specify, the Wikipedia article on fornication cites this:
https://en.wikisource.org/wiki/The_New_International_Encyclopædia/Fornication
Just curious, but is this “breach of promise” in any way related to the saying “it’s a woman’s prerogative to change her mind?” I have heard that saying my whole life and never have been given a decent explanation as to what it meant. In light of this thread, however, it seems that perhaps the saying grew out of the idea that if a man promised to marry a woman, he couldn’t back out without consequence, but she could.
Or, does that saying originate from something else altogether?