The Brexit probe is part of a broader reckoning that Facebook, Twitter Inc. and Google’s YouTube are facing globally, as governments come to grips with the companies’ far-reaching influence on society, as well as vulnerability to manipulation.

Damian Collins, the chairman of the digital, culture, media and sport committee that’s leading the investigation, said social media companies must be more proactive in investigating the misuse of their services rather than wait for prodding from regulators. "They are best placed to investigate activity on their platform," he said.

Twitter, which has until Thursday to offer its own response to U.K. lawmakers, declined to comment.

Also on Wednesday Twitter said it would begin notifying U.S. users who had been exposed to Russia propaganda. In a hearing in Washington, U.S. lawmakers pressed executives from Facebook, Twitter and YouTube to act more aggressively to prevent the spread of terrorist-related content.

Responding to a broadening backlash, Facebook Chief Executive Officer Mark Zuckerberg has vowed to "fix" the social network, and last week made changes to its main news feed to ratchet back posts from businesses and media outlets in favor of those from friends and family.

Eoin Treacy's view

There are a number of aspects to this story. The first from a British perspective is if Russian tampering in the Brexit vote is proven then it would lend support to those looking to hold another referendum. The basis of course being that the first plebiscite was tainted by propaganda which was also a charge during the campaign. I doubt it would overturn the decision.

Meanwhile, there appears to be increasing acceptance within the EU that the only way to plug the hole in the budget left by the UK is to ensure they keep paying into the bloc’s coffers. That represents quite an incentive for the EU to eventually agree to a negotiated settlement lest the UK parliament shoot down what is brought to it.

In the meantime, the Pound continues to rally against the Dollar and is now testing the psychological $1.40 level. Perhaps more importantly it is now testing the region of the trend mean against the Euro and a sustained move above €1.14 would signal a return to demand dominance.

The backlash of the establishment against anti-status quo candidates and causes represents a threat to social media companies. Facebook is tinkering with how news is prioritized in response to this evolving story but the trend remains broadly consistent, with support being found in the region of the trend mean on successive occasions.

Alphabet (Google) remains in a staircase step sequence uptrend.

Twitter has been a wallflower since shortly after its IPO but increasingly has base formation completion characteristics.

These charts suggest investors have a broadly sanguine attitude to the developing investigation into the role played by social media in swaying elections. In fact, what one can conclude is that these advertising venues are highly effective so it could be good news for sales.