LONDON — After several months of scandal within Britain’s opposition Labour Party over its handling of anti-Semitism in its ranks, investigators in London said on Friday that they have opened a criminal inquiry into accusations that some party members posted anti-Semitic threats online.
The Metropolitan Police commissioner, Cressida Dick, said in an interview with BBC Radio 4 that officers were looking into online posts by Labour members that amounted to more than just offensive comments. The police are consulting with prosecutors at this stage of the investigation.
“We are now investigating some of that material because it appears there may have been a crime committed,” she said.
Ms. Dick said that the Labour Party itself was not under investigation, and that while she hoped political parties policed themselves on issues like anti-Semitism, officers had an obligation to look into such allegations.
The comments — coming from a small number of Labour’s roughly 540,000 members — would not have attracted so much notice had the party not faced criticism for months for a failure to address what many contended was anti-Semitism. The party’s reputation has also suffered because of past remarks by its leader, Jeremy Corbyn, that were seen as endorsing anti-Semitism.
The online posts were part of a dossier of Facebook comments and other statements obtained by the radio station LBC that included 45 cases of suspected anti-Semitism by Labour members. Of those, four warranted a criminal investigation as hate crimes, according to Mak Chishty, a former Metropolitan Police investigator in charge of hate crimes who reviewed the documents for LBC.
The radio station said the dossier included a message stating, “We shall rid the Jews who are cancer on us all,” and another threatening a “Zionist extremist” lawmaker with “a good kicking.”
When LBC handed Ms. Dick a copy of the dossier after an interview in September, she turned it over to hate crimes specialists who started investigating, she said.
It was not clear whether the comments were made by obscure rank-and-file Labour members or elected officeholders. Ms. Dick declined on Friday to offer any details about what or how many crimes may have been committed, except to say the law set a high bar for online posts to be deemed criminal.
A Labour official said the party had already been reviewing some of the allegations when Ms. Dick was given the dossier. But it was not clear what disciplinary action, if any, Labour has taken against the party members accused of writing the posts.
The party’s executive committee approved a plan in September to double the size of its disciplinary body, responding in part to concerns from Jewish leaders that Labour was slow to deal with allegations of anti-Semitism.
“The Labour Party has a robust system for investigating complaints of alleged breaches of Labour Party rules by its members,” the party said in a statement. “Where someone feels they have been a victim of crime, they should report it to the police in the usual way.”
Tensions over anti-Semitism within the party were stoked this summer when Labour’s executive committee voted not to adopt the full text of the working definition of anti-Semitism as set out the International Holocaust Remembrance Alliance.
In particular, the committee declined to endorse several examples of what the alliance defined as anti-Semitism, including describing Israel’s existence as a racist project and accusing Jewish people of being more loyal to Israel than their home country.
The committee tried to calm a growing furor in early September by reversing itself and adopting the full text. It also tried to make clear that this should not prevent criticism of Israeli government policies, particularly toward Palestinians.
Mr. Corbyn has also been accused of anti-Semitism, particularly since it emerged this year that in 2012 he had endorsed a mural that was widely considered anti-Semitic — something for which he has since apologized.