Stephen Schwarzman, chief executive of the private equity group Blackstone, has warned that the widening gap between Wall Street's lavish pay packages and middle America's stagnating wages risks causing a political and social backlash against the US's new rich.

The comments by Mr Schwarzman, whose fortune has been estimated at $2.5bn by Forbes magazine, are a reminder to the financial community that the success of the past few years is causing deep unease among America's middle classes.