The party's co-leader Patrick Harvie also suggested plans to dual the A9 and A96 could be scrapped, with the money instead used to provide free bus travel for young Scots.

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Mr Harvie has written to Finance Secretary Derek Mackay - who has still to set a date for the 2020-21 Scottish budget - outlining the kind of measures he wants to be included to enable the six Green MSPs to back the minority SNP administration in its tax and spending plans.

Since losing an overall majority in the Scottish Parliament, the SNP has relied on the Greens to get its proposals through Holyrood.

Mr Harvie said this year ministers must produce a budget that will help tackle the climate emergency.

In his letter to Mr Mackay, the Scottish Green co-leader calls for increased investment in the low-carbon economy, including a "significant increase" in spending on improving home energy efficiency in a bid to help cut greenhouse gas emissions, as well as funding for renewables projects.

Mr Harvie demanded a "transformative shift in public investment", calling on the the Government to switch away from road building and instead spend more on public transport and initiatives to encourage walking and cycling.

He suggested free bus travel could be provided for young people, with the funding for this coming from scrapping planned spending on roads "such as the dualling of the A9 and A96 and the proposed £120 million Sheriffhall roundabout" outside of Edinburgh.

The letter says: "The Scottish Greens also believe that reductions in the working week would help to demonstrate that the Scottish Government is committed to a fairer economy that is focused on well-being rather than unsustainable growth.

"Public-sector trials of a reduced working week could form part of the public-sector pay settlement for 2020-21, and we believe that public-sector unions would be open to discussing this possibility."

Mr Harvie stressed that to win Green support "this budget must turn the rhetoric of a 'climate emergency' into a reality by increasing investment in the low-carbon economy".

In previous years, the Greens have pressed the Finance Secretary on issues such as local government funding and changing Scotland's income tax system.

Mr Harvie said his party is "proud of the impact" it has had in these areas.

He added: "Despite the constraints on this year's budget process, we will again challenge the Scottish Government to go further on our priorities and seek meaningful change.

"I want to be clear that the urgency and seriousness of the climate emergency means that we cannot vote for a 2020-21 budget that does not meet the ambition set out in this letter."

Mr Mackay was due to set out his tax and spending plans for the upcoming financial year in December but put plans on hold until after the UK Government announces its own Budget, which will include a cash allocation for Scotland.

There has been speculation Chancellor Sajid Javid will not set out his proposals until March, with Mr Harvie branding the delay from Westminster "irresponsible".

The Green MSP said: "The UK Government is creating a potential crisis by delaying its own Budget and the Scottish Government's task in responding to that irresponsible behaviour is not easy.

"However, this must not be used as an excuse for a budget which lacks ambition for Scotland.

"Our proposals for the next budget would see transformative investment in tackling fuel poverty, public transport and new green industries that will help tackle the climate crisis and create jobs for communities across Scotland.

"Derek Mackay has the power to tackle the climate emergency, he needs to accept the responsibility."

SNP told to trial reduced working week to secure support from Scottish Greens