The plinth of the World War Two leader's statue on Parliament Square was sprayed in yellow paint with the words "is a racist".
"We have arrested a man in Parliament Square on suspicion of causing criminal damage to the Winston Churchill statue," the Metropolitan police said on Twitter.
The statue was defaced in June during a fractious end to a mostly peaceful protest over the death of African-American George Floyd in Minneapolis, prompting authorities to board it up for a period.
Floyd's death in police custody in May sparked protests about racial inequality across the United States and Europe and reignited a debate in Britain about monuments to those involved in the country's imperialist past.
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