The organiser of a 400-person wedding at a Charedi school on Thursday evening faces a £10,000 fine.
Guests fled the site of the event, the Yesodey Hatorah Senior Girls School in Stamford Hill, after police arrived to break up the gathering.
Officers said they found covered-up windows and clear evidence a wedding had taken place.
The organiser made admissions on the scene and is facing a £10,000 fine. Some guests were issued £200 fixed penalty notices.
Footage shared with the JC showed heavy police presence in the area.
One person tweeted in response: "As an NHS worker I am utterly lost for words! We will never be out of this pandemic with events like this. PLEASE, follow the guidelines and stay at home! NHS workers are exhausted!"
Detective Chief Superintendent Marcus Barnett, Central East BCU Commander, said: "This was a completely unacceptable breach of the law, which is very clearly in place to save lives and protect the NHS. An NHS that is under considerable pressure at a time when Covid 19 has killed nearly 100,000 people. This is a deadly and very dangerous disease. We can all see that and we must act responsibly.
“People across the country are making sacrifices by cancelling or postponing weddings and other celebrations and there is no excuse for this type of behaviour. My officers are working tirelessly with the community and we will not hesitate to take enforcement action if that is required to keep people safe.”
There is no suggestion the school was aware of the event.