Your guide to tactical voting in the general election

"Voting is meant to be easy," writes John Curtice, professor of politics at Strathclyde University in today's i.

"You decide which party you like the most, and mark an X against the name of that party's candidate in your constituency."

But what if you can't decide between two or more parties, but do know who you do not want to win. In that instance it might make more sense to vote for the party that, locally at least, stands the best chance of defeating the party you don't want to win. Welcome to tactical voting.

The above map shows the 77 seats where tactical voting is likely to determine whoever becomes the local MP, and potentially the overall result of the general election.

Most of the instances where your enemy's enemy is your friend involve battles between Labour and the Tories, but the Lib Dems are also involved in a fight for survival in the south-east with their former coalition allies. Finally, Labour is desperately trying to avoid a Scottish National Party whitewash, but may only do so with Lib Dem and Tory support.

Conservative-Labour battles (majority)

Conservative-SNP battle (majority)

Liberal Democrat-Conservative battles (majority)

Liberal Democrat-Labour battles (majority)

Liberal Democrat-SNP battle (majority)

Labour-SNP battles (majority)

More: [What happens after the election? Six possible outcomes in the event of a hung parliament]1

Quiz: [How much do you really know about the 2015 general election?]2