Mr. Faruq was also concerned that the government might further stigmatize Muslims by expanding the country’s already powerful antiterrorism legislation. “Now there is a lot of talk about nonviolent extremism,” he said. “What does that mean? If you don’t believe in a certain way, you are extremist? Everything is extremism now.”

He pointed out the way the news media had been quick to identify Finsbury Park Mosque as a former hotbed of radicalization. He wondered if that was appropriate. “It just takes away that little bit of sympathy,” he said.

Details matter. That is something many people here said on Monday. It was Muslims, awake because of Ramadan, who saved a lot of lives in Grenfell Tower by waking up neighbors and alerting the fire department. And it was an imam of the Muslim Welfare House who helped form a protective ring around the van driver on Monday before the police arrested him. “How many people know that?” asked Omar Hussain, a community worker.

Language matters, too. When The Daily Mail initially described the assailant outside the mosque as a “white van driver” rather than a terrorist, Muslims were not alone in their indignation. J. K. Rowling, the author of the “Harry Potter” books, criticized The Mail, an influential right-wing tabloid, for the way it referred to him. “The Mail has misspelled ‘terrorist’ as ‘white van driver,’” she wrote, but later deleted, on Twitter. “Now let’s discuss how he was radicalised.”

One answer, said Jacob Davey of the Institute for Strategic Dialogue, who analyzes extremist online narratives, is that Islamist militants and far-right extremists have fed on one another’s hatred to recruit people for their causes.

After the Grenfell fire, the English Defense League posted an image of the tower on Facebook (later removed) with the caption: “They say Ramadan saved Lives. It would be the first time Islam saves lives.”