The Green party does not believe people should be banned from joining ISIS or Al Qaeda, its leader has revealed.

In an extraordinary claim, Natalie Bennett said people should not be punished for what they think and stressed it should 'not be a crime simply to belong to an organisation'.

More than 600 people from Britain are thought to have travelled to Syria and Iraq to join jihadists, with security forces warning returning fighters pose the biggest terror threat to Britain.

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Natalie Bennett said people should not be punished for what they think and stressed it should 'not be a crime simply to belong to an organisation'

The Green party has seen a surge in support in recent months, doubling from 5 per cent saying they would back them in October to 10 per cent in a recent YouGov survey.

Party membership has also risen dramatically, with the Greens claiming to have overtaken both the Lib Dems and Ukip, bolstered by a row over whether Miss Bennett should be included TV election debates.

What we want to do is make sure we are not punishing people for what they think or what they believe Green party leader Natalie Bennett

But after years in the political wilderness, few people know what the party stands for, beyond its environmental credentials.

Green Party policy states 'it should not be a crime simply to belong to an organisation or have sympathy with its aims, though it should be a crime to aid and abet criminal acts or deliberately fund such acts'.

On BBC1's Sunday Politics Miss Bennett was challenged about the policy and whether that would make it legal for people living in Britain to join brutal terrorist groups such as ISIS.

She said: 'This is a part of our policy that I think dates back to the age of the ANC and apartheid South Africa.'

Pressed on whether that meant it would be allowed to be a member of Al Qaeda or IS, she said: 'Exactly. What we want to do is make sure we are not punishing people for what they think or what they believe.

'Obviously actions of inciting violence, supporting violence, those are absolutely unacceptable, illegal and should be pursued to the full extent of the law.'

She added: 'What we are talking about is a principle that you shouldn't be punished for what you think. And we need to balance, we do not protect freedom by destroying it.'

Security agencies warn Britain faces a severe threat posed by extremists inspired by ISIS fanatcis in Iraq and Syria

CAMERON TO FEATURE IN DEBATES David Cameron will take part in TV election debates, the Tory party chairman indicated yesterday. Grant Shapps said discussions were 'edging towards a solution' and that the Prime Minister 'wants the debates to happen'. The move comes after broadcasters issued a 'take it or leave it' warning that the debates – now involving seven parties – would go ahead with or without the PM. Advertisement

Membership of ISIS was formally banned when it became prescribed organisation last summer.

Security minister James Brokenshire said at the time: 'Proscription is a useful weapon in the armoury at the disposal of the government, police and security service to disrupt terrorist activity and protect the UK.'

On Thursday, Foreign Secretary Philip Hammond warned Britain is at 'very significant risk' from a terror attack by extremists inspired by ISIS jihadis.

Speaking ahead of a counter-terror summit in London, he warned against complacency in the fight to 'disrupt these plots before they come to the stage of an attack'.

Mr Hammond stressed the danger of terror attack in the UK by people inspired by ISIS, also known as IS and Isil.

He said: 'We have to regard Isil as probably the greatest single immediate threat to Britain's national security at the moment.

'There's a very significant risk of an Isil-inspired attack being planned and, if we are not successful in intercepting it, executed by Isil sympathisers who live in the UK but are inspired by what is going on in Iraq and Syria.'

A YouGov survey last week put the Greens on 10 per cent, up from 5 per cent when the Labour party set up a unit designed to tackle the threat of the minor party

RISING GREEN TIDE COULD COST LABOUR 22 SEATS AT ELECTION A surge in support for the Green party cld cost Labour 22 seats, a polling expert has warned. The Greens have been boosted by a row over TV election debates, with David Cameron refusing to take part if the Greens were excluded. Labour fears it could lose vital left wing votes to the smaller party, including former Lib Dem supporters. Robert Ford of the University of Manchester, carried out analusis of local election results 2010. It found 22 marginal seats Labour needs to win or cling on to where more than 10 per cent of voters are identified as being Labour/Green-inclined. It includes Lib Dem strongholds such as of Bristol West, Norwich South and Cambridge, Tory-held Hove, and Brighton Kemptown, and Labour-held Birmingham Edgbaston and Tooting. Mr Ford told The Observer: 'The voters fuelling the Green boom share one characteristic with supporters of the Ukip and SNP insurgencies – a deep-seated disaffection with the political establishment. 'Besides the general problem of disaffection, Labour also faces a specific problem with the Greens into political competition. 'Young, highly educated, cosmopolitan liberal idealists, Greens are more or less the polar opposite to Ukip's ageing, socially conservative, nationalist electorate. Labour is losing votes to both, but any policy that appeals to one pole will anger those at the other.' Advertisement

Mr Hammond added: 'Of course, our security and intelligence agencies, our police forces are working tirelessly around the clock to monitor, to identify, to intercept and to disrupt plots of this nature, and we've been very successful in doing so, but we mustn't be complacent.

'We know there are people out there who wish us harm and we have to be vigilant and we have to work extremely hard to make sure we identify and disrupt these plots before they come to the stage of an attack.'

Police and security officials have warned Britain is facing an 'almost inevitable' attack by fanatics who have been 'militarised' by ISIS.

Miss Bennett also set out the Greens' views on defence, which include scrapping the Trident nuclear deterrent, leaving Nato and cutting the size of the armed forces.

'We obviously need to be able to defend our own borders, civil defence, and we have a real responsibility as a rich country to contribute to UN peacekeeping forces,' she said.

Asked if that meant a home defence force, she said 'yes' but would not give figures on how many personnel that would require.

On immigration policy, she said in the 'medium term' the party's policy was to progressively reduce UK immigration controls.

She added: 'What we want to do now is allow people who should have the right to be in the country, to be in the country. What we have to do is stop the race to the bottom on immigration rhetoric that we have been hearing, led by Ukip and sadly followed by the other (parties).

'People who should have a right to be here - which means asylum seekers and refugees - we are not treating them properly and we need to.

'British people who want to live with a foreign, non-EU spouse or partner here, on the Government's own figures 19,000 Britons can't live in their own country.

'We saw last year the number of foreign students applying to British universities going down.

'All of those are things that are causing real damage to people's lives.'