Winton Capital, the $4.2bn (€3.5bn) London hedge fund manager, has closed its flagship fund to new investors after nearly trebling its overall assets in 2005.

David Harding, Winton's founder, said he had wanted to slow the growth of the Winton Futures fund, the firm's largest, after it reached $1.9bn. He said: "We want to put a brake on asset growth. My nightmare is that we become an asset gathering company, I want to avoid that."