Open this photo in gallery: Protesters wave Israeli flags and hold placards in front of Elizabeth Tower, commonly known as Big Ben, at the Houses of Parliament, in central London on Nov. 26,JUSTIN TALLIS/AFP/Getty Images An estimated 50,000 demonstrators against antisemitism marched in London on Sunday to protest against a rise in hate crimes against Jews since the attack by Hamas militants on Israel in October and Israel’s subsequent bombardment of Gaza. Protesters carried placards bearing the messages “Shoulder to shoulder with British Jews” and “Zero tolerance for anti-Semites.” Others showed the faces of Israeli hostages held by Palestinian militant...