Fully agree with James. What he says about Marshall's notion of "real" competition is possibly one of the reasons (let's say the theoretical reason, though hardly the main one) for the conspicuous absence of a formal antitrust law or policy in Britain in the late 19th - early 20th century. The Marshallian view immunized Britain for a long time against the nirvana fallacy of the PC model underpinning most antitrust practices in US and Europe. 
Nicola Giocoli 
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