“I believe we will be the most influential party of the 21st century,” Green co-leader Jonathan Bartley told his party conference in Yorkshire earlier this week.

The bold claim is a necessary morale boost at a time when Jeremy Corbyn’s Labour Party is sucking away Green members and votes. At the last general election the party's vote share fell in key target seats such as Bristol West, where it was down 14 per cent.

But Bartley’s boast also has weight. From promoting renewable energy, to attacking the lack of action on air pollution, Green positions often put the government on the backfoot – and have public opinion behind them.

Not least on Brexit. Together with the Lib Dems, the Green Party is calling for a second referendum on the terms of any deal for leaving the EU.

Speaking at the recent conference, the Green MEP Molly Scott Cato stressed that this was not an attempt to undermine democracy – but to reinforce it: “We are asking for more democracy, not less. We are asking for a democratic choice between two real, possible futures at the end of the Brexit negotiations: the deal, or remaining a member of the EU.”

Any hope of securing a beneficitial Brexit for Britain has already been undermined by the government’s own anti-democratic approach to the process, she adds over the phone a couple of days after her speech.

Scott Cato describes the government's trade plans, shared in the last few days, as “guff”, and says far greater transparency is urgently needed:

“Sure, there are ways we could improve things which we couldn’t do while we’re part of the EU,” she says. “But we can only do them if we’re living in a genuine democracy where our representatives are informed and listen to us and have the power to make change. And at the moment I’m afraid the government isn’t making that possible.”

Of particular concern is that the EU Withdrawal Bill presently asks MPs to vote for an “empty box” on Brexit's terms, incuding things like the border with Ireland and the UK's debts. Once that bill is passed, she says, the country will have signed up to leaving the EU no matter how bad a deal the Conservatives bring back from Brussels.

If the government thought they could secure a good deal for the UK, they would ask MPs to vote once the terms were defined, Scott Cato believes. Instead, she thinks the fact they are asking for the vote before a deal is reached, having committed to Brexit whatever the cost, spells trouble. “We have to stop Brexit before Christmas. Or it’s going to be incredibly difficult, as things get worse, to change our minds.”

For these reasons, the Greens are pressing hard for a second referendum. And according to Scott Cato, the best time for this would be October next year. This date would be the latest the UK government could leave defining a deal if it is to travel through the European Parliament in time for the March 2019 deadline.

But what if a second referendum in 2018 becomes riddled with the same uncertainties as the first? A new trade deal would take even longer to agree than the divorce deal.

“That’s the risk we face," Scott Cato responds, "but the truth is once we’re out of the EU, we’re out of the EU.”

Even if a later trade deal fell through and we decided we wanted to return, there’s no certainty that France wouldn’t exercise their veto, she warns. “We’ve totally burned our bridges with Europe now, and the second referendum is the last chance of us not being out in the cold for a decade or more.”

And how confident is she that a second referendum would go the way of Remain?

“I think people do have a clearer idea of what [being] outside the EU means now and the risks that it entails,” she says. “We've seen the fall in the pound, and we've seen the loss of jobs, the companies saying that they're going to move overseas ... We’ve seen that it's not possible to pick off one member state against the other, that they won't let us have our cake and eat it, and they've seen that we're not going to get £350m for the health service – and I could go on a long time here, couldn’t I!”

“I have to trust the people - I'm a democrat,” she adds. “But I have to trust the people to make a decision between A and B. Not between A and Not-A. Not just bundling up all their frustrations and blaming them on Brussels.”