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Bio fuels were once seen as the answer to global warming and dwindling oil stocks.

Today, many who took that line believe instead, that they increase pollution and are behind worldwide environmental havoc, rising food prices, worsening hunger and poverty.

The first official hint of changing attitudes came in the Gallagher Review of 2007, which expressed concerns that bio fuels - renewable liquid fuels derived from plant or animal material – not only didn't help climate control, but were making poor people in the developing world even poorer.

Then, bodies as diverse as the World Bank and major charities defined bio fuels as "a crime against humanity" and "a silent tsunami". Some alarming facts also emerged – for example, that the grain required to fill the tank of a Range Rover with ethanol is sufficient to feed one person for a year, and that American land turned over to bio fuel production every two years alone would fill 250 million mouths.

But that is not the whole story. Governments and multi-nationals fight what they see as a simplistic black-and-white approach, insisting that bio fuels remain our best hope for the future - despite some damaging side-effects. Scientists meanwhile, are working on ‘a second generation’ of bio fuels which they believe, could eradicate those side-effects.

For this documentary, investigative reporter Gerry Northam finds out exactly how much bio fuels cost and who is paying for it.

He visits Paraguay, where the expansion of the soy industry has happened in tandem with the violent suppression of small farmers and indigenous communities. It's being alledged that farmers are being bullied into growing soy with pesticides at the expense of their food crops, health, farms, and – in many cases – their lives.