LONDON — Jeremy Corbyn’s decision to celebrate Passover with Jewdas, a self-described radical leftist Jewish group, has been heavily criticized in Britain, where his opposition Labour Party has been accused of tolerating anti-Semitism.

The group’s very name — a play on Judas, the disciple who betrayed Jesus Christ — is a provocation, one that has angered many of those encountering the group for the first time. Some critics say that Jewdas’s name, and antics, risk stoking age-old myths and hatreds that have led to anti-Semitic violence.

Created in London more than a decade ago, Jewdas is a group of left-wing activists who are at odds with most of Britain’s mainstream Jewish organizations. Its members say they are opposed to capitalism and fascism, but the group may be best known for its vociferous criticisms of Israel and its policies toward Palestinians.

“It’s a radical diaspora Jewish group that has taken an explicitly non-Zionist stance, alongside satirizing the many absurdities of the British Jewish community and throwing excellent parties,” according to a founder of the group, Joseph Finlay.