Under Boris Johnson's current plan the UK will continue to follow EU rules until the end of December 2020, while the two sides try to work out a lasting trade deal.

But the Greens - who are contesting 22 constituencies north of the Border at next month's poll - argue that Scots must be given the option of independence rather than remaining in a UK state outside of the EU.

Speaking at the party's manifesto launch in Govan today, co-leader Patrick Harvie said it was "entirely rational" to offer another referendum on the country's constitutional future as "Scotland did not vote for Brexit".

Patrick Harvie said Scots should have the option of voting for independence before the end of any Brexit transition period. Picture: PA

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"If Brexit can't be stopped - and we still think it can be - it's perfectly reasonable to say on that timescale, when every other country has a say on our future, that Scotland should also have a say.

"If Scotland was to vote for independence in that timescale, then we have the option of ensuring our entry into the European Union as an independent country can be smooth. I think it would be a mistake to leave until after that transition period.

"I do want to stress however that we think Brexit can be stopped, and should be stopped."

Cabinet minister Michael Gove yesterday insisted there would be no extension to the proposed transition period if the Conservatives remain in power following the election.

The Scottish Greens have failed to return a single MP at previous Westminster elections but are urging voters to back them to ensure the climate crisis is pushed further up the political agenda.

The party's 2019 manifesto includes proposals to limit pay inequality, including the introduction of a pay ratio - which would see a 10 to 1 pay ratio introduced in the public sector, and a commitment to phase it in for private sector firms too.

This would take the form of a legally-binding Corporate Governance Code, limiting the total amount paid to CEOs relative the pay to a fixed multiple of ten times that of their average employee.

The current median CEO pay in a FTSE100 company, including salary, bonus, long-term incentive plan, benefits, and pension contributions, for the financial year ending 2018 was £3.46million a year.

Other measures in the manifesto include the phasing in of a four-day week and expanded trials of a universal basic income, a non-means-tested monthly payment to everyone, which would remove stigma around poverty and provide a better safety net than the deeply flawed UK welfare system.

Scottish Greens co-leader Lorna Slater said: “The average FTSE 100 CEO earns 117 times more than the average UK worker. It’s not right that bosses earn factcat salaries when their employees are finding it harder to get by.

“Not only is the growth of wealth inequality a gross injustice, it is also devastating for our planet.

“People can’t think about their carbon footprint when they are starving, but let’s be clear, it isn’t the poor who are speeding up global warming. A celebrity millionaire has a carbon footprint of 10,000 times the average person. As for Billionaires with private jets, they have the power to distort our democracy.

“We urgently need to address this imbalance. For example, studies show a four-day week for a living wage would not only give people more quality of life and allow them more time with their family, but it would also improve productivity.

“A more equal society is not only fairer, it helps us reduce emissions."

Scottish independence: IndyRef2 must take place before end of Brexit transition period, say Greens