The UK Office of Fair Trading is worried about the market for large company audits:
The OFT has been concerned for some time that this market is highly concentrated, with substantial barriers to entry and switching.
As a result, the OFT announced today (July 29, 2011) that it has provisionally decided to make a reference of the market of large company audits to the UK Competition Commission. Under Section 131 of the UK Enterprise Act of 2002, the OFT may make such a reference if it
has reasonable grounds for suspecting that any feature, or combination of features, of a market in the United Kingdom for goods or services prevents, restricts or distorts competition in connection with the supply or acquisition of any goods or services in the United Kingdom or a part of the United Kingdom.
I don't teach, either US or comparative, antitrust, but I do remember that the key issue is the definition of the relevant "market." Wholly apart from whether the UK sub-market is really a separate market, I wonder about the ability of national governments to force changes in international markets. Perhaps the only that will happen is the UK large companies will just move their "headquarters" out of the UK. If that's not enough, they might also reorganize so that they no longer are organized under UK law.
Hat tip: UK Corporate Law and Governance blog.