Facebook users will be able to share the news that they have voted - without revealing who for - thanks to a new button that will appear on polling day to encourage turnout.

The I'm a Voter button will appear at the top of the site's newsfeed tomorrow, and the 35 million Facebook users in the UK will be able to click it to share with friends the news that they have voted in the General Election.

The button has been used in the previous three US elections, as well as EU elections and the Scottish referendum last year.

When used in the Indian election last year, the megaphone symbol used in the button reached 31 million people, with more than four million sharing that they had voted, said the social network.

Facebook says previous studies have found that conversation on the site ahead of voting can increase turnout, revealing that 300,000 extra voters turned out at the polls in 2010 US presidential election having seen Facebook posts from their friends.

The social media giant, which has more than 1.4 billion monthly active users globally, also revealed that the most discussed election issue is the economy.

Between January 1 and May 1, there have been more than 4.5 million interactions relating to the economy on Facebook says the technology giant, with Europe and immigration the next most discussed topic.

The economy was the most discussed topic in 350 of the 651 constituencies.

Facebook also revealed the most talked about issues in each of the party leaders' constituencies.

Health was the most-discussed issue in the Witney constituency, where Tory leader David Cameron is standing.

The biggest issue for voters in Doncaster North, where Labour leader Ed Miliband is a candidate, was Europe, as is the case in both South Thanet and Rochester and Strood, where Ukip's Nigel Farage and Mark Reckless are standing.

Facebook users in Sheffield Hallam, where Lib Dem leader Nick Clegg is a candidate, were found to be discussing the economy most.