Immigrants would be given a regular cash payment by British taxpayers without needing to become citizens, under plans drawn up by the Green Party. Documents reveal that the left-wing outfit, currently polling at 18%, would hand a monthly payment of up to £1,600, called Universal Basic Income (UBI), to anyone in the country without settled status, or who have a non-visitor visa.

The party's boss, Zack Polanski, said such a scheme would be worth around £1,200 to £1,600 per month. Setting out his plans in a 2024 article for the Big Issue magazine, he said: "A universal basic income policy is simple yet transformative: it would ensure every citizen receives an unconditional recurring payment. While the exact amount is up for debate, it would broadly align with the minimum wage - around £1,200 to £1,600 per month."

Figures released by the Migration Observatory suggest that as of 2024, just over 1 million non-british nationals are likely to hold temporary non settled leave to remain in the country. It would mean at the higher end of the UBI amount the treasury would need to pay out £1.6bn a month, or £19.2bn per year, to pay for the policy.

Critics blasted the move as "madness", with shadow home secretary Chris Philp telling the Daily Express: "We should not be handing taxpayers' hard-earned money to migrants who have only just arrived in the UK and never made any contribution whatsoever."

The Tory shadow minister insisted illegal migrants should be "deported not given handouts", saying that the Green Party "has gone completely insane".

Katie Lam, a Conservative shadow minister, said that the promise of UBI for migrants meant that "the Green Party are proposing a magnet for uncontrolled migration" which would be funded by "hard working British taxpayers already under pressure."

Mr Polanski has unveiled a string of policies since becoming leader of the Green Party last year. They include bringing in rent controls and capping the earnings of the highest paid in a company to a maximum of 10 times the lowest paid staff member.

He has made tackling the "affordability crisis" a key plank in his attempts to woo voters, and is riding high in a combination of sustained good polling and a recent by-election victory in Gorton and Denton which saw Hannah Spencer MP become the first of his party to earn her seat outside of a nationwide poll.

Ms Lam slammed the Green Party, saying they planned to start "writing blank cheques that undermine public confidence, turbocharge illegal migration and strain services" which she said was a "recipe for chaos at the border and resentment at home.".

Migration watchdogs joined the criticism, with Alp Mehmet, the boss of Migration Watch UK said it was "another set of beyond-daft proposals from the flaky, far-left Greens - whatever happened to saving the planet Mr Polanski? There seems to be no limit to how far you will go to pick the pockets of the British taxpayer."

Free market think tank, the Adam Smith Institute (ASI) likewise branded the policy as one which "ignores basic reality."

The institute's Joanna Marchong told the Express: "This latest chapter in Zack-economics raises the same questions we've always had: how can we afford it, and who does this really benefit?"

She added: "At a time when the welfare bill is already spiralling, adding another vast, unconditional entitlement risks pushing the system beyond breaking point and undermining incentives to work and contribute.

"Instead of chasing expensive policies that expand blanket entitlements, policymakers should be removing the incentives that keep people out of work and on welfare."

The Green Party was approached for comment.