A man has been arrested and 26 people reported for £800 fines after police broke up a party on a canal boat.
Some 30 people were discovered on the vessel on the River Lea in east London at about 04:20 GMT.
The Met said a 31-year-old held on suspicion of breaching Covid health protection regulations had previously been reported for a £10,000 fine over another boat party.
The partygoers were dispersed and the boat has been seized.
Ch Insp Pete Shaw said it was "incredibly disappointing that incidents of this nature continue".
"To have an individual who has repeatedly ignored these regulations and who appears to have organised multiple events is dangerous and indicates a complete disregard for the safety of all involved," he said.
Met Police officers also shut down another large party in a house in Wandsworth, south-west London, on Thursday night.
About 30 to 40 people were found at the gathering shortly before 23:40.
One woman was arrested for breaching Covid regulations while a man was held for an unrelated offence.
Fixed-penalty notices were issued to the other attendees found there.
Insp Matt Ebbs said: "These are challenging times but we must all play our part, and I urge everyone to follow the rules to protect themselves and their community."