Recent elections have shown that likes and shares on social media giant Facebook are translating into votes for political parties at an increasing rate.

But while Facebook is “one of the, if not the most important channel” of the media, there are “massive question marks” about the transparency of political parties and campaign groups’ usage of it, Carl Miller, research director of the Centre for the Analysis of Social Media (CASM) at thinktank Demos, told CNBC via telephone. Miller asserted that governments need to regulate political parties’ use of Facebook, and make transparent their spending on the platform.

Social media as an increasingly effective tool for mobilizing the masses has caught the attention of regulators. Information Commissioner Elizabeth Denham, head of the U.K.’s independent authority on public information, wrote in a blog post in May this year that a formal investigation was opening up into “the use of data analytics for political purposes.” While the post, like much official material, referred social media with a broad brush, it is widely accepted that Facebook is the most influential. The investigation chiefly concerns campaigning ahead of the Brexit referendum in June 2016, but “potentially also in other campaigns.”

Effective use of social media helped transform the fate of the underdog U.K. Labour party in the General Election earlier this month. An uplifting campaign, which encouraged legions of young voters to head to the polls, meant that the party added 33 parliamentary seats to its total and helped to erase the majority held by the incumbent Conservative Party.

Facebook’s potential power over elections lies in its ability to enable political parties and campaign groups to specifically target individuals with advertising. Users are confronted with a closed circle of information, one that is uniquely geared to influence them in a less publicly accepted way than newspapers and television channels.

The extent to which governments regulate Facebook’s impact on political outcomes remains a grey area. In fact, the Information Commissioner’s Office mentions social media only a handful of times in its latest guidance on political campaigning. The social media behemoth does have its own code of practice. The issue is seemingly playing on Facebook’s conscience, and in a blog post by the company entitled “Hard Questions” published June 15, one such topic was “Is social media good for democracy?”

Miller questioned the argument that the extent of Facebook’s influence is limited to younger demographics, saying instead that “If it didn’t matter, why are parties spending so much money on it?” According to the U.K.’s Electoral Commission, the Conservative party forked out £1.2 million on social media advertising ahead of the 2015 General Election, though both parties are yet to confirm their 2017 spend to CNBC.

Simple logic of numbers suggests that targeted campaigning could make a big impact in electoral systems that divide voters into smaller areas, such as the U.K.’s constituencies, where a small margin of voters can cause a seat to swing from one party to another. Miller said that Facebook’s “algorithmic accountability (is) more powerful than any newspaper in the world” and that governments “should be looking to change that.”

Facebook clarified to CNBC via e-mail that it aims to strike a balance between allowing businesses and organizations to advertise while also making sure that its users are comfortable. Data remains private and is not sold to or shared with third parties, but advertisers can reach people based on interest categories.

There is interest among internet users in the influence of political campaigning on the advertisements they see. Who Targets Me is a browser plugin which identified such political advertisements in the General Election just gone. Sam Jeffers, founder of the software, told CNBC via telephone that “we’re coming to a place in the U.K. where we have large volumes of political advertising,” and “Facebook is the biggest marketplace.” Come election day, 11,700 people had installed the plug in.

Effective use of social media was a part of the success of Momentum, a grassroots campaign group for the Labour party. The group’s latest press release said that its use of the technology had “helped win previously unwinnable seats for Labour.” According to the release, its viral videos reached nearly 30 percent of U.K. Facebook users, with little capital behind them. “The vast majority of traffic is organic, with Momentum spending less than £2,000 on Facebook advertising over the course of the election,” it said.

Joe Todd of Momentum told CNBC via telephone that he “(didn’t) think that Facebook is the extent of political organizing,” saying instead that “knocking on doors is the most important thing.” Content “only goes far if lots of people decide to share it,” he added.

But Ryan Holmes, CEO of social media management firm Hootsuite, told CNBC last week that effective use of Facebook in elections was a trend which applied to the successful campaigns of former U.S. President Barack Obama, as well as Canadian Prime Minister Justin Trudeau and U.S. President Donald Trump.

“Politics and elections are being won by the winner’s savvy-ness of and use of social … it’s about listening, it’s about not being tone deaf to the electorate and being able … get your message out there.”

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