On my internet travels this morning whilst doing my daily Family Lore Focus news update I came across this story, which surprised me. I didn't realise any civilised countries still had the crime of adultery on their statute books. According to Wikipedia, New Hampshire is not the only US state that does (apparently about half still do), with penalties varying from a scary life sentence in Michigan (do they have any room left in their prisons?) to a rather more reasonable $10 fine in Maryland.
All of this set me to doing a little research regarding adultery as a crime in this country. Now, correct me if I'm wrong, but it seems that adultery was not a crime here until that well-known killjoy Oliver Cromwell passed the Adultery Act in 1650, which quite reasonably imposed the death penalty "in case any married woman shall ... be carnally known by any man (other them her Husband) (except in Case of Ravishment)". According to this report in Hansard (discussing, of all things, the Child Support Bill), the Adultery Act did have one slight flaw: it insisted that conviction should require that the crime be committed in the presence of two witnesses...
Unsurprisingly given his record, Charles II repealed the Adultery Act when he was crowned and, as far as I am aware, adultery has never been a crime in this country since. However, according to this article adultery: "has been, theoretically at least, punishable in England by virtue of unwritten law in the ecclesiastical courts, though the offence has never been pursued with any great or systematic vigor". Amusingly, the article continues: "and it may be remembered that Blackstone charges the framers of the canon law with an improper levity in respect to this sort of offences from their own aptitude to commit them."
Lastly note that, despite its wonderfully euphemistic name, 'criminal conversation' was not a crime, but a tort. [For those who have not heard of it, criminal conversation was a civil suit by which the plaintiff claimed damages against the defendant who had committed adultery with the plaintiff's spouse. I understand that this also still exists in some US states, but it was abolished in this country in 1857.]