Facebook could face growing pressure over its role in politics, as campaigners cite the significance of its' role in both Brexit and the US election.
Leave campaigners and Trump supporters both tell BBC Panorama that the social media giant was decisive roles in their victories.
And in an investigation to be aired tonight, one of parliament's senior voices on media regulation questioned whether the rapidly expanding network should face more questions over its accountability.
US Republicans spent around $70m on Facebook marketing ahead of last year's presidential election, while Leave.EU political strategist Gerry Gunster says: “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.”
Facebook is already working directly with the UK's political parties ahead of June's vote. And videos that appear in people’s news feeds can be promoted by political parties and campaigners.
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But Tory MP Damian Collins, who chaired the Culture Media and Sport select committee, will tomorrow warn that other broadcasters face strict rules on partiality and restrictions on advertising.
“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,” he says.
The social media site says it complies with all regulations that apply to it, and is committed to assisting civic engagement and electoral participation.