Tens of thousands of people marched through central London Saturday to protest against the far right, weeks ahead of local elections and six months after Britain saw one of its largest far-right demonstrations. Organized by hundreds of civic groups, including trade unions, anti-racism campaigners and Muslim representative bodies, Saturday’s Together Alliance event was billed as the biggest in UK history to counter right-wing extremism. Some leading British Jewish groups accused the march organizers of failing to include the Jewish community in its demonstration, although several left-wing Jewish organizations did take part, marching together as a bloc. A separate pro-Palestinian march...