The Liberal Democrat promise to revoke Article 50 is "arrogant" and "self-indulgent", former Green Party co-leader Caroline Lucas has told ITV News.
Speaking to ITV News Political Correspondent Paul Brand on his Acting Prime Minister podcast, the MP for Brighton and Pavillion said the pledge to effectively cancel Brexit is "dangerous" and "imperils democracy".
Ms Lucas insisted her criticism wasn't based on fear of losing votes to Jo Swinson's party, which is pitching itself as the natural home for Remain supporters at the next election.
Asked whether it made it harder to form a Remain election pact with the Lib Dems - which would see the parties agree not to compete for particular seats - she demanded a greater commitment from her closest political rivals.
Ms Lucas told Brand the Lib Dems and Labour both needed to show a genuine intent "to help some Green Party voices to get into Parliament" after she felt let down by her party's sacrifices in the 2017 election.
The full podcast interview will be released on Thursday.
Ms Lucas spoke to ITV News on the same day Lib Dem leader Swinson told Robert Peston her party's Brexit stance is "based on what we think is right, it's based on our values and our principles".
Asked by Brand if the Greens would also revoke Article 50, Ms Lucas said: "Absolutely not. I am deeply concerned about this policy of revocation as a first resort rather than as the very, very last as we're just about to tip out of the EU.
"It imperils democracy ... I think it's arrogant, I think it's self-indulgent."
She added: "Obviously (the) Lib Dems have done some polling that tells them that this is the right policy in terms of some short-term votes but in terms of the long-term harm that I think this will be, that will be done to our country through doing this.
"I think that it's incredibly dangerous. I'm deeply worried by it."
Ms Lucas, who stepped down from the party co-leadership last year, runs a project 'Dear Leavers' to speak to Brexit voters across the country in the hope of finding common ground.
In the podcast the MP went on to add: "We're already such a divided country.
"By saying to 17.4 million people 'we're not listening to you and we don't care why you voted leave and we're just going to put the clock back to the 22nd June 2016', I think that is the biggest kick in the teeth that you could possibly deliver."
The Greens will push at the next election for a People's Vote to rerun the EU referendum and would campaign in favour of Remain again.
Asked if she would work with other parties to bolster the chances of Remain-supporting MPs being elected, Ms Lucas accepted it would have to be a two-way street in agreeing to stand down candidates.
"Essentially we made a big gesture in 2017 (not to stand in certain constituencies) and we paid a high price for it, quite frankly," she said.
"We're not expecting to win as many seats as those other much bigger parties but there needs to be ... an element of reciprocity in this for sure."
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Catch up with past episodes of Acting Prime Minister:
- Emma Lewell-Buck on accents and siding with Farage over Swinson
- Chuka Umunna on his 'messy' year and why Change UK failed
- Mark Francois on losing his dad and his pre-Brexit epiphany
- Anna Soubry opens up on pain of Umunna split and why Boris 'isn't fit to clean loos'
- 'Boris Johnson should have backed up ambassador' says Nicky Morgan as Acting PM
- Stella Creasy overhauls 'Hogwarts gone wrong' Parliament and ditches manifestos
- Labour's David Lammy justifies comparing Tory Brexiters to Nazis and defends Comic Relief 'white saviours' criticism
- Justine Greening on her bid to be Tory leader and calling Mark Zuckerberg
- Jacob Rees-Mogg backs Boris Johnson while outlining his own vision for the nation
- Why Ben Fogle would scrap exams and reintroduce national service
- Heidi Allen is 'too emotional' to be PM but wants Nick Clegg on her team
- Campaigning mum Hannah Deacon tackles medicinal cannabis in Number 10
- Sarah Champion on prostitution, pushing the nuclear button and Tinder dating
- Ben Bradley on exam obsession, getting kicked out of school and forgiving his digital past