The Met said that officers were called on Sunday afternoon to find about 100 people gathering in Ray Lane, Southwark, in what appeared to be a pre-planned protest.
"This sort of gathering is specifically prohibited under the tier four restrictions brought in following the recent rapid rise in cases," Acting Inspector David Smith said in a statement.
"We all have a responsibility to follow the rules, stay at home as much as possible, and help stop the rapid spread of COVID-19 in our city," he added.
"Anyone coordinating intentional breaches on this scale should know they risk very significant financial penalties," he said.
The Met said that the organiser, a 58-year-old man, will be reported for the consideration of a fixed penalty notice of up to £10,000.
London is currently under tier four restrictions to curb the spread of the CCP (Chinese Communist Party) virus, following the discovery of a new variant of the virus that authorities say is more infectious. Residents have been told to stay at home unless they have a "reasonable excuse" to leave their houses.
Under the Health Protection Regulations 2020, gatherings organised by a business; a charitable, benevolent, or philanthropic institution; a public body; or a political body can take place if the organiser carries out a risk assessment that satisfies regulations and takes all reasonable measures to limit the risk of transmission.
On Dec. 19, the Met arrested 29 protesters after they allegedly refused to cooperate with police.
The Met said on Dec. 20 that the female organizer of one of the protests, which was attended by around 150 people, had been reported for consideration of a £10,000 fixed penalty notice.
Three men, Christmas Fallah, 35, Joss Lillis, 27, and Leon Larose, 28, "have been charged under Health Protection Regulations with participating in a gathering of two or more people. All three men were also charged with assaulting an emergency worker," the Met said in a statement.
"The majority of the other 26 people arrested were issued with fixed penalty notices for breaching Health Protection Regulations. A number of other people attending the protest were also issued with fixed penalty notices but were not arrested," the statement reads.