The idea that Russia may have tried to influence last year's Brexit referendum isn't new, with both Facebook and Twitter seemingly being used to spread anti-EU propaganda. The Electoral Commission is currently investigating the possibility, and has asked Google for its cooperation.
The Commission has already been investigating Facebook and Twitter's alleged role in the interference, but a letter sent from Facebook seemingly reveals that Google is also being investigated and has been asked to cooperate - something Business Insider confirmed with the EC, though Google didn't comment.
Google has been fairly quiet in wake of revelations that Russia may have been interfering with the US election and Brexit vote, with most of the heat falling on Facebook and Twitter for seemingly facilitating the work of professional Russian trolls. It has confirmed, however, that Russian accounts did buy adverts for YouTube and Gmail in the run up to the US election last October. So it's no surprise that the EC wants to work out if something similar happened here.
Both Facebook and Twitter have confirmed that they will assist in the EC's investigation, with Twitter's UK Policy Chief Nick Pickles promising to share information uncovered in its own inside investigations. Though both companies have downplayed the role their services may have played, multiple investigations have found that Russia-linked accounts did get a significant amount of engagement. Hopefully the EC's investigations will help work out just how effective that engagement was.