LONDON — In the annals of British political protest, the giant balloon is the current weapon of choice.
On Saturday morning, a Briton who says the mayor, Sadiq Khan, is not doing enough to fight crime returned the favor and launched a giant balloon of Mr. Khan near Westminster on Saturday.
The new 29-foot inflatable is the idea of Yanny Bruere, who says he is a free-speech advocate incensed by rising crime. On his crowdfunding page, he wrote: “In light of the Donald Trump ‘Baby Trump’ balloon being allowed to fly over London during his visit to the U.K., let’s get a ‘baby Khan’ one and see if FREE SPEECH applies to all and whether or not Mr. Khan and the London Assembly will also approve this.”
He added, “Under Sadiq Khan, we have seen crime skyrocket to unprecedented levels. People in London don’t feel safe and they aren’t safe, 81 murders this year alone! Khan Out.”
A small crowd cheered and shouted, “Higher! Higher!” on Saturday morning as the balloon took to the sky, wobbling as if buffeted by a breeze. It depicted a scowling Mr. Khan lying on his side, one hand behind his head, wearing a yellow bikini.
The mayor addressed the planned balloon launch in a segment on ITV London on Thursday, saying: “If people want to spend their Saturday looking at me in a yellow bikini, they’re welcome to do so. I don’t really think yellow’s my color though.”
A group of online investigators called Bellingcat has linked Mr. Bruere to deleted Twitter accounts that spread anti-Semitism and conspiracy theories. The idea of a Khan balloon was celebrated online by pro-Trump and pro-Brexit groups, and by anti-Islam commentators in the United States and Britain.
Mr. Bruere did not immediately respond to a request for comment on the Bellingcat claims sent by Facebook message on Saturday. But he told Sky News that the “tweets were taken out of context” and that the accounts had been deleted over eight months ago. He also criticized what he said were attempts to penalize him for exercising his right to free speech.
To Twitter commenters who called the brown-skinned, hooknosed balloon image of Mr. Khan a racist caricature, Mr. Bruere replied: “Should we have made him white? Or black? So you could then accuse us of ‘cultural appropriation.’ ’’
He also wrote: “How can I be ‘far right’ for doing the EXACT same thing the Trump organizers did? They do everything they can to silence you if you don’t fit in with the agenda.”
A spokesman for City Hall did not reply to an email asking if officials had been aware of Mr. Bruere’s background when he was granted permission to fly the Khan balloon.
By Saturday, the crowdfunding page had raised more than 59,000 pounds, over $76,000, for Mr. Bruere’s “Make London Safe Again” campaign. The slogan echoes the Trump presidential campaign slogan, “Make America Great Again.”
The original balloon plan seems to have been to fly a “baby Khan” inflatable dressed in a diaper, like the Trump version. The bikini is apparently a reference to the mayor’s decision in 2016 to ban what officials called body-shaming advertisements, such as the “Beach Body Ready” campaign depicting a woman in a yellow bikini that was posted in the London subway.
Pro-Brexit groups such as British Voice, the American anti-Muslim activist Pamela Geller and the British writer and provocateur Katie Hopkins promoted the balloon launch online. Ms. Hopkins wrote on Twitter this past week: “Dear @POTUS — You’ll love this great work by @YannyBruere — demanding Sadiq Khan #MakeLondonSafeAgain. Khan does NOT speak for TRUE Brits.”
The mayor and Mr. Trump have had a long-running feud: Mr. Khan has lashed out at Mr. Trump for his inflammatory remarks about Muslims, and Mr. Trump and his son Donald Trump Jr. have accused the mayor of being weak on crime and terrorism.
After a long period of steady declines in violent crime, London has experienced a spike this year, with the city averaging in excess of three killings a week.
Analysts say that the surge in violent crime has been driven by factors like drug gang rivalries, cuts to youth services and social programs, and the ease with which teenagers can now taunt and provoke one another on social media.
In April, after six people were killed in shootings and stabbings in seven days, Mr. Khan said he supported the use of “targeted” stop-and-search by the London police. Hundreds more officers were deployed across the city. In June, lawmakers introduced the Offensive Weapons Bill to ban online sales of several types of tactical knives.
Those behind the balloon campaign seem to have been tickled by the fact that any inflatable depicting Mr. Khan would have to be approved by the mayor’s office to fly near Parliament. On Thursday, a spokesman for the mayor said that City Hall had, indeed, given Mr. Bruere permission to fly the balloon near Parliament Square Garden from 9:30 a.m. to 11:30 a.m. local time.
The Metropolitan Police and the National Air Traffic Services also signed off, according to the BBC.