Narendra Modi is to pay his first visit as India’s prime minister to his country’s former colonial master, Britain, this week. He’ll meet Queen Elizabeth II at Buckingham Palace, address Parliament, have a sleepover at Prime Minister David Cameron’s country estate and star in one of his trademark stage shows with the Indian diaspora at Wembley Stadium.

The red-carpet treatment represents a rehabilitation for Mr. Modi after years in the U.K’s dog house. Britain distanced itself from Mr. Modi after 2002 religious riots killed...