Police broke up a house party with more than 30 guests at a property in central London in the early hours of Sunday morning.
A total of 34 people were fined for breaking Covid rules, with the organiser facing a penalty of £10,000.
Guests at the party on Dover Street in Mayfair were playing music and drinking alcohol when the Metropolitan Police arrived at 12:52am, the force said.
Superintendent Daniel Rutland said: “As we prepare for more restrictions to be eased in England it is more important than ever that everybody is following the rules and avoiding unnecessary risks.
“We all have a part to play to ensure the Covid infection rate does not rise again and this type of behaviour risks jeopardising the progress that has been made by the majority of people who have followed the rules.”
From Monday, non-essential shops and outdoor attractions like zoos and theme parks will reopen, as will gyms, self-contained accommodation and personal care businesses like hairdressers.
Pubs and restaurants may serve customers in outdoor seating areas, but only in groups of up to six from multiple households or more from two households.
Large groups will not be allowed to meet indoors until 21 June at the earliest.
