Facebook is expected to play an influential role in the General Election, amid concerns about a lack of regulation.
Leading members of campaigns which backed the UK's bid to leave the EU and Donald Trump's presidency told the BBC's Panorama that the social network played a decisive part in the outcome of the Brexit vote and the US election, with Britain's upcoming poll thought to follow suit.
The unprecedented use of the site by the campaigns allowed them to single out specific audiences with targeted posts, the strategists said.
Gerry Gunster, political campaigner at Leave.EU, hailed Facebook as a "game changer" and said: "You can say to Facebook, I would like to make sure that I can micro-target that fisherman in certain parts of the UK so that they are specifically hearing that if you vote to leave that you will be able to change the way that the regulations are set for the fishing industry.
"Now I can do the exact same thing for people who live in the Midlands who are struggling because the factory has shut down. So I may send a specific message through Facebook to them that nobody else sees."
Gary Coby, director of advertising for the Republican party, echoed the targeting strategy and told Panorama that Facebook helped a Trump win by allowing the campaign to target users through their personal data, including email addresses and phone numbers.
He said: "The way we bought media on Facebook was like no one else in politics has ever done."
Around 70 million US dollars (£54 million) was spent on the site by Mr Trump's official campaign, Mr Coby said.
Simon Milner, policy director at Facebook UK, said political parties enlisted specialists from the firm to help maximise their use of the site.
The social network also provides a virtual Facebook Elections service to help parties craft their online campaigns.
Critics have expressed concern at the unregulated nature of Facebook's role in politics.
Thirty-two million people in Britain have an account, with many unaware of the site's use for politically sponsored posts which appear as adverts, or as posts on users' feeds.
Damian Collins, chairman of the Culture, Media and Sport (CMS) committee who earlier this year led an inquiry into the spread of fake news, called for the site to be more accountable.
He told the BBC: "Historically there have been quite strict rules about the way information is presented and broadcasters work to a very strict code in terms of partiality and there are restrictions on use of advertising.
"But with something like Facebook you have a media which is increasingly seen as the most valuable media in an election period but which is totally unregulated."
Far-right group Britain First, which has 1.6 million Facebook followers, told Panorama that on several occasions it paid the social network to promote its videos.