The Greens will today call for a blanket 20 per cent "sugar tax" on soft drinks to tackle obesity, a measure estimated to collect $500 million a year.

The move, which would add about 20 cents to the supermarket price of a can of Coca-Cola, could lead to a fall in consumption of 12 per cent, according to research cited by the Greens.

Globally, the push to tax sugary drinks has been led by British celebrity chef and healthy eating ambassador Jamie Oliver, who in March challenged Australia to "pull your finger out" and back the tax.