The weather is cold in New York but the temperature is rising in the boardrooms of big companies. Hedge fund investors, who prefer to be known as shareholder activists these days, are assaulting the managements and strategies of US companies such as Time Warner and General Motors.

General Motors is taking notice of Kerk Kerkorian, the billionaire investor who has taken a 9.9 per cent stake and wants it to fix its entrenched problems in the US. It is considering offering his holding company a seat on its board. Meanwhile, Time Warner is trying to fend off the attentions of Carl Icahn, who holds a smaller stake in the company but talks louder.