Image copyright Getty Images Image caption A Green Party pledge could see every adult paid £72 a week

Every adult in Britain would be paid a basic income regardless of wealth or earnings, the Green Party will say in a commitment to appear in its manifesto.

But Natalie Bennett, the party's leader in England and Wales, told the BBC a Citizens' Income of £72 a week would take time to implement.

In February, the party's only MP, Caroline Lucas, said the policy was only a "long-term aspiration".

Critics have suggested it could cost £280bn.

Ms Bennett told BBC Radio 4's Today programme that as "the sixth richest economy, we have to provide for everyone's basic needs and we have to do that within the limits of our one planet".

She said this "very big change" would be one of the party's election pledges.

"The Citizens' Income, the commitment to that, is in this manifesto - but we've seen the difficulties that Iain Duncan Smith has got into in introducing Universal Credit, so we're saying it would take more than the term of one parliament to actually introduce this," she said.

Policy guide: Welfare This election issue includes access to benefits (apart from pensions), poverty and inequality.

The Green Party is looking to substantially boost its representation in Parliament amid predictions of another hung Parliament.

"We are now the third largest political party in England and Wales," Ms Bennett told Today.

"We're larger than UKIP, we're larger than the Lib Dems. We have more than 58,000 members.

"We've had one Green MP, Caroline Lucas, who's had a huge impact as one MP in the Parliament.

"And we're now working very hard to send a strong group of Green MPs to Parliament who - given the electoral arithmetic - have a very good chance of being in a strong position to really influence the whole direction of the next government."

She said her party offered a "genuine alternative" to the Conservatives' "austerity heavy" and the Labour's "austerity light".

The party is launching its election manifesto next week.

The BBC poll tracker indicates that on 4 April, the Greens had a 5% share of the vote (Conservatives had 34%; Labour 33%; UKIP 13%; Liberal Democrats 8% and others 6%).

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