Nicola Sturgeon's "ally" Green leader Natalie Bennett has pledged to end tax cuts for the North Sea in her party's General Election manifesto.

The Greens also said they would phase out other fossil fuel subsidies, in a bid to help the planet.

First Minister Ms Sturgeon has been staunch in her support for the oil and gas industry, currently under pressure because of falling worldwide oil prices.

Together the SNP, Plaid and the Greens have been described as a "progressive alliance" during the election campaign.

All three will take on Labour leader Ed MIliband as part of the BBC's Challengers TV debate on Thursday night.

The Green manifesto also included pledges to create one million quality jobs and rebuild public services by ending austerity, as well as to renationalise the railways and ban night flights.

Ms Bennett also said that Green MPs could put pressure a future UK government to scrap the Trident nuclear weapons system on the Clyde.

She told her activists this was a landmark election for the party, as polls suggesting a surge in support for the Greens.

Earlier she reiterated that the party did not plan to enter any formal coalition arrangement if there is a hung parliament after May's election.

She said: "We've ruled out any kind of support to a Conservative government but we would look at supporting a minority Labour government on a case-by-case basis.

"That would give us a real opportunity to push Labour on the policies we know the public wants and which are at the heart of our manifesto - whether that's scrapping nuclear weapons or reversing the privatisation in our NHS, whether that's returning local schools to local control or bringing rail back into public ownership."

She hailed what she said was a "new kind of politics" where the economy and society could be run for the many and not the few.

"It sees the end of the disastrous policy of austerity that is making the poor, the disadvantaged and the young pay for the greed and the fraud of the bankers.

"This is a vision that is exciting increasing numbers of Britons."

The party also pledged to scrap a £15 billion roads programme south of the border and give students free public transport.

Caroline Lucas, former Green Party leader and the only Green MP in the last parliament, said tackling the environmental crisis is not "some luxury that is only possible when there are good economic times".

She added the issue could not be discarded when times are tough "like that extra cappuccino on the way to work".

The Green have come under pressure to explain how they would fund their policies.

Ms Lucas said there was money available but it was a question of society's "choices".

Last month Ms Sturgeon told an audience in London: "If you live in England I think there is an argument for voting Green."

Critics accused her of risking Scotland's economy with her support for the party.

But an SNP spokesman said that accusation was "ridiculous" and that the First Minister "obviously stands for the policies and manifesto of the SNP, not any other party".