When India votes in a general election next year, the poll will be the world's largest democratic exercise and the biggest-ever test of the role of social media in an election.

As the ruling Bharatiya Janata Party (BJP) readies for battle with the newly energized Congress party-led opposition in the election, which must be held by May, the role of Facebook, Twitter and WhatsApp could be crucial in deciding who wins.

India already has close to 900 million eligible voters, and an estimated 500 million have access to the Internet. The country has 300 million Facebook users and 200 million on Facebook's WhatsApp messaging service — more than any other democracy. Millions use Twitter.