Multiple journalists have seen Ms. Kuenssberg with a guard this week, although she and the BBC both declined to comment, or to confirm or deny the news. Others spoke of how her experience was part of an international trend in which public discourse has become more venomous, and trust in mainstream journalists has eroded.

Her case has some parallels with the intimidation of journalists at rallies during President Trump’s election campaign, in particular of Katy Tur, an NBC correspondent who was protected by a Secret Service agent as she left a rally in 2015 at which the future president had singled her out for criticism.

But Ms. Kuenssberg’s treatment has a specifically British context. Unlike in America, the threats of violence against her and other journalists have not followed rhetorical attacks by leading politicians — Mr. Corbyn himself condemned online abuse in a major speech on Wednesday — but have instead come from members of the public.

“We are worlds apart from the kind of systematic abuse of the media that Trump engages in,” said Robert Peston, the political editor of ITV, one of the BBC’s main commercial rivals. “There’s not a single occasion that I can think of where Corbyn has said anything critical of Laura Kuenssberg, so it’s very different to the Trump situation in that sense.”

Ms. Kuenssberg’s trolls are also as likely to come from the left as the right — as are other critics of her work. Her reporting, as well as that of many other BBC journalists, is the subject of constant critique on a wave of new left-wing websites, such as The Canary, Evolve Politics and Novara Media.