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The leader of the Greens has admitted hard-left activists have flocked to her party – but denies its recent membership surge was due to ­infiltration.

Natalie Bennett says the Socialist Workers Party recruits are a “tiny” proportion of its 60,000 members.

Yet several will play an important role during the election and her own partner is an ex-SWP ­stalwart.

“There may be some prominent ones,” she tells the Mirror. “But as a proportion it’s absolutely tiny and factional and as we grow bigger that proportion is getting smaller.

“Our young Greens have proportionally increased in size. The SWP is not strong among the young.”

Labour leader Neil Kinnock fought a famous battle with Militant in the 80s but, asked if her party has been targeted by similar “entryism” tactics, Ms Bennett insists: “Absolutely not.”

A rising Green tide – some polls put their support as high as 11% – is a problem for Labour. And a split on the left is still David Cameron’s best chance of election victory in May.

This weekend the RMT rail union’s president announced he will stand for the Greens in Lib Dem seat Redcar.

Peter Pinkney said he was attracted to the party by its plan to ­renationalise the railways and other left-leaning policies. Those policies include a 35-hour week, a £10 a hour minimum wage and plans to hand every man, woman and child £72 a week guaranteed “citizens’ income”, rich or poor, so “no-one falls through the cracks”.

In fact the anti-austerity message seems more important to the party than its green roots these days – Ms Bennett barely mentions the environment once in our interview. It’s a winning formula which has chimed with Greek voters, and the Syriza coalition’s poll victory there last month is a big boost for the radical left.

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Ms Bennett says: “We have very much welcomed the Syriza result. Austerity has failed. This has to stop. We have to stop the poor, ­disadvantaged and young paying for the errors of the bankers.”

Despite sharing his antipathy towards bankers, Aussie-born Ms Bennett, 48, appears to view support from Russell Brand as a hindrance rather than a help. The Greens’ only MP, Caroline Lucas, had praised the comedian for “rattling” Parliament’s cage, but Ms Bennett warned a “big personality... tossing their hair around would be a distraction”.

She is also keen to clarify her stance on ISIS, after suggesting it should not be illegal to support the group. She said: “I may not have made it as clear as I meant to: ISIS is a hideous, horrific organisation and any sort of ­involvement or membership is supporting terrorism and violence and should be illegal.”

But despite being mocked for fantasy politics, Ms Bennett remains optimistic.

She says: “If we can offer real change and people get engaged in it we can have a peaceful revolution, we can have an election that looks like no other then all the predictions go out the window”

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