Sir Martin Sorrell, dubbed the Sage of Soho for his views on the economy, warned he has yet to see signs of a sustainable upturn and there is little hope of a return to booming growth any time soon.

"We don't see any green shoots," he said at the World Economic Forum in Dalian, China. Sir Martin, chief executive of WPP, the world's largest marketing company by revenue, forecast a V-shaped economic recovery in China but was more cautious about other parts of the world.

He said advertising spend will remain subdued and warned that clients "won't invest again until they are sure" of the recovery.

His views were echoed by others at the summit with the majority of business leaders fearing the current recovery is not sustainable.

Christopher Kearney, chief executive of US industrial equipment maker SPX Corp, said: "What we're seeing now is the slowing of declines. We don't think there's going to be any significant recovery in 2009. We certainly don't subscribe to any kind of a V-recovery theory." He said it will be "a slow, more steady recovery".

Stephen Roach, Asia chairman of Morgan Stanley, said Asian consumption needs to rise since the US is unlikely to return to pre-crisis spending levels.

"The American consumer is dead money. This is the wake-up call for export-dependent China and Asia," he said. "There is no way that the large population mass in Asia is going to compensate for the shortfall in US consumption demand."