WITH the election starting gun cocked, the main political parties are set to unleash a barrage of expensive television, radio and print advertisements partly paid for by donations from Australia's biggest companies.

But corporate largesse to political parties corrupts democratic processes and should be banned, say critics who have called for an overhaul of campaign funding.

In the 2004 federal election, the Liberal and Labor parties spent an estimated $40 million on advertising, with much of the money coming from big corporations and unions. For both parties, private funding contributes more than 80 per cent of their multimillion-dollar budgets.