With 211 million followers on social media, the multibillionaire seems intent on using his global platform to rattle British politics.

Elon Musk, the billionaire backer of Donald J. Trump, had been promoting Nigel Farage. But on Sunday Mr. Musk said Mr. Farage “doesn’t have what it takes.”

In a barrage of posts rife with misinformation, he revived questions about a child sex abuse scandal, vilified the prime minister and defended a jailed far-right agitator.