At 11.30am on Monday, a change to the law was introduced that bans two people from different households in England gathering in an indoor, private place during the coronavirus lockdown.
The amendment to the Health Protection (Coronavirus, Restrictions) Bill states: "No person may participate in a gathering which takes place in a public or private place indoors, and consists of two or more persons."
Previously, going to another person's home to have sex would have been a breach of coronavirus lockdown restrictions, but now both parties could be prosecuted under the law. Having sex in public is already illegal.
Only those with a "reasonable excuse" are permitted to meet in a private place.
The amended bill reads: "No person may, without reasonable excuse, stay overnight at any place other than the place where they are living."
This differs from the previous legislation, which prohibited people from leaving their home at all without a reasonable excuse.
Anyone breaking the law can be fined £100, halved to £50 if paid within 14 days.
Human rights barrister Adam Wagner tweeted on Sunday: "I can't believe I'm about to tweet this.