How do other rich countries' antitrust laws compare to America's?

Since Teddy Roosevelt and Taft, American government has taken an active role in busting monopolies and creating competition where competition has not arisen under the free market. Some major corporate giants have been affected, notably AT&T and MicroSoft. Do the world’s other rich countries do the same thing, and if so, are their laws tougher or less tough than America’s?

I hear occasionally of the zaibatsu in Japan or the chaebol in South Korea, but I’m not sure if these are monopoly trusts in the old 19th-century American sense, or just very large companies that still have effective competition.

Apparently antitrust laws are pretty strong in the EU.
Europe Sets Antitrust Sights on Google Search

Letters to The Economist: Antitrust policy in Europe Among others:

Thanks, I’d about given up on getting any answers.

The link to the Economist mentions that Intel was targeted by antitrust prosecutors in Japan and South Korea too, which suggests that the EU is not the only one with antitrust laws at least as vigilant as the US. (Apparently the US has also targeted Intel for antitrust violations).

The word ‘trusts’ is not used here, at least not in this context.
The Monopolies & Mergers Commission currently investigates such cartels and may order them broken up. Various industry regulators can also investigate; Oftel has several times investigated British Telecom’s monopolistic position and may yet require it to be broken up.

Oftel? , that organization disappeared a years ago. I think you mean Ofcom