The Greens hope to win over parent voters by promising to double child benefit to £40 ($61) per week in England and Wales.

At the moment, a parent can typically claim £20.70 a week for the oldest or only child (under 16) and £13.70 for an additional child.

"It's bold policies like these that set the Green Party apart from others. We don't offer half-measures, or minor changes," said Amelia Womack, the deputy leader of the Greens.

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"In the midst of such struggle in this country, the Green Party are offering something unique: hope. We make this one very clear promise to voters: we will always stand for an economy, a society, that works for the many, not just the few."

The left-of-centre party have also pledge to keep Independent Living Fund, which provides money to help disabled people live an independent life. The policy would cost around £300m.

The announcement came after the Tory Chancellor George Osborne and the Institute for Fiscal Studies (IFS) warned that a Conservative government would "almost certainly require significant cuts to some of the main benefits".

The pledge come with just days to go before the general election on 7 May, with the Tories one point ahead of Labour (35% vs 34%) in the latest opinion poll from YouGov.

The Greens, however, have dropped to 5% from the 8% they garnered earlier in the year.