The U.K.’s competition regulator is looking into Microsoft’s Activision acquisition and how Amazon treats its third-party sellers. Sound familiar? That’s because other countries — including this one! — have been investigating these companies for months and even years. But as the saying goes, “the party don’t start till the CMA walks in.” Or something like that.

The Competition and Markets Authority is a rather thorough investigator that’s made Big Tech nervous before, and it’s not afraid to get help from its neighbor. The regulator said it’s working with the European Commission on its investigation into Amazon. And when it does decide to look into Big Tech issues, its decisions have a track record of being highly consequential.

• In December, the CMA ordered Facebook and Giphy to break up. Advocates for competition scrutiny applauded the U.K.’s analysis for going deeper than other competition regulators and taking aim at so-called “vertical” deals. “That’s a really good thing and something that I hope U.S. enforcers take note of,” Public Knowledge’s Alex Petros told my colleague Ben Brody when the breakup happened.
• The CMA also reached a deal with Google earlier this year giving regulators more power over the company’s privacy plans. An ad tech exec called it “the start of a journey toward more public oversight of big tech promises” at the time.

The U.K. isn’t sleeping on Big Tech’s moves, and sometimes it’s ahead of other regulators in its investigations, like the one into Nvidia’s flopped bid to buy Arm. Even though the CMA decided to open new probes after others this time around, it might be the one everyone should look out for.

— Sarah Roach (she/her/hers)