Fresh fears emerged today that the Government will be £79million short of funds for Olympic athletes by 2012.

The Government is increasing its spending to £600 million overall but had been expecting the private sector to stump up a chunk of the cash.

Today advertising tycoon Sir Martin Sorrell warned that businesses - other than the main London Games sponsors - were reluctant to fund athletes because they could not see what benefits they would get in return.

Although the main Olympics sponsors can use their logos prominently in 2012, firms that back the new government scheme cannot even have their logo on athletes' shorts.

Sir Martin told the BBC that the Government's plans were "going to need much more definition for our clients to be interested".

Tim Crow, chief executive of Synergy, a sponsorship consultancy that advises companies including Coca Cola, said ministers' plans were in "a bloody mess" and didn't have "a cat in hell's chance" of raising the £79 million in the current credit crunch.

Olympics minister Tessa Jowell claimed that the figure was a "soundly-based ambition". "We have announced our intention. Let's come back in 18 months' time and review the position then," she said.