The Metropolitan Police said it received reports of a large gathering on a moored boat on Saturday evening.
Officers arrived at the venue in Volt Avenue, North Acton, at 2300 GMT local time and saw more than 70 people at the party.
A total of 72 people have been reported for the consideration of a fine after they attended a party on a boat in #Ealing last night.
DCI Thomas Bowen said: “”This was a blatant breach of the Coronavirus rules that are in place to save lives.”https://t.co/QCzGh0O3eR
— Metropolitan Police (@metpoliceuk) January 31, 2021
The £800 fine, which was introduced last week by Home Secretary Priti Patel, applies to those who attend gatherings of more than 15 people in homes.
The organiser of the boat party was identified and will face a £10,000 ($13,705) fine, police said.
Detective Chief Inspector Thomas Bowen said the party “appears to have been organised on social media.”
Also on Saturday, Essex police broke up a house party at a vacant rental property, which was attended by 18 people.
— Essex Police (@EssexPoliceUK) January 31, 2021
When officers attended the venue in Bury Road, Sewardstonebury, at 1700 GMT, they were initially refused entry from those inside who claimed to be making a music video, police said.
When they finally got inside, the officers found 18 individuals “clearly having a party while others were still arriving at the property.”
All 18 people present were fined £800 each for breaching CCP (Chinese Communist Party) virus restrictions and an investigation is under way to establish who organised the event, said the police.
The UK has been under varying levels of CCP virus restrictions since the pandemic began last spring.
Earlier this month, Prime Minister Boris Johnson put the whole of England under the third national lockdown to curb the spread of a new variant first detected in southeast England, which he said had a higher transmissibility than the old variant.
Police forces, including the Metropolitan police in London, have said they are taking a stricter approach to enforcing the lockdown rules.
Martin Hewitt, chair of the National Police Chief Council, said on Jan. 13 that he would make “no apology” for the almost 45,000 fixed penalty notices that had been issued against rule-breakers.
Simon Veazey, Mary Clark, and Lily Zhou contributed to this report.