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.
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.’