Anti-poverty campaigners set up a tropical island on the South Bank on Friday to encourage Londoners to lobby the prime minister before the G8 summit.
The Enough Food For Everyone IF campaign claims that developing countries lose billions of pounds to tax havens each year.
The campaigners allege that many multinational companies shift their profits made in the developing world into tax havens.
Passers-by were urged to tweet a message to David Cameron calling on him to "sort out shady tax havens" at next week's G8 summit.
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