Prime Minister Keir Starmer of Britain on Monday fired back at Elon Musk after days of inflammatory social media posts by Mr. Musk, the billionaire owner of X, indirectly accusing him and others of “spreading lies and misinformation” about victims of child sex abuse gangs. “Those who are spreading lies and misinformation, as far and as wide as possible, are not interested in victims,” Mr. Starmer told reporters at an event south of London dedicated to repairing the National Health...