The Scottish Green manifesto will propose removing the “pomp and pageantry” of the monarchy under independence, co-leader Patrick Harvie has said.

Speaking ahead of the party’s campaign launch in Edinburgh on Thursday, Mr Harvie has said his party will set out plans for a written constitution and a republic which can elect and remove heads of states.

The manifesto plans are set to propose the abolition of “unelected heads of state” and a “permanent written constitution” in an independent Scotland.

He said: “The monarchy is a badly outdated and fundamentally undemocratic institution. It represents a different era and feels increasingly irrelevant and ridiculous in the 21st century.

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“Yet in a matter of weeks the full pomp and pageantry of monarchy will be on display when the King does the state opening of a new government.

“We should be able to challenge power and elect or remove our head of state through the ballot box, like most countries do.”

He went on to demand a written constitution which would be used to “avoid the kind of power grabs and stunts we have seen from Westminster”.

“The Scottish Greens are the only party that is calling for an independent Scottish republic where power lies with the people rather than being banded down like a family heirloom.”

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The Greens set out the policy ahead of their manifesto launch in Edinburgh tomorrow and as the SNP unveil their document today.

A paper published last year by the Scottish Government, part of a series making the case for independence, proposed that Scots could get a vote on whether or not to keep the monarchy if the country becomes independent.

It also put forward the case why Scotland should have a written constitution in line with the 27 members of the European Union and other states around the world.

Under the plan a vote for independence would see the Scottish Parliament develop an interim constitution.After independence, a constitutional convention would be established to develop a permanent written constitution, with this to be considered by Holyrood and also put to the people in a referendum.

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The policy paper stated: "It is the Scottish Government's policy that independence in itself would not result in a change to the Head of State, and that initially an independent Scotland would remain a constitutional monarchy. 

"This would be the case for as long as the people of Scotland wish to retain the monarchy. The Scottish Government believes that the Constitutional Convention is the appropriate place to consider other models for the Head of State of an independent country."

Speaking to journalists after launching the document the then First Minister Humza Yousaf was asked if the process would mean Scots being given a vote on keeping King Charles III as head of state.

Mr Yousaf replied: "Hypothetically, that is what our constitutional convention seeks to do. I am not going to prejudge what our constitutional convention will say or what it will do.

"But it could look at and probably will look at whether we have the right model as regards head of state. The permanent constitution proposal would be put to people in a referendum."

The policy marked a change from the Scottish Government's position ahead of the referendum in September 2014 when it supported keeping the monarchy as head of state under independence and did not offer the prospect of a vote on whether the historical arrangement should be kept.

During last year's SNP leadership contest Mr Yousaf said he favoured an elected head of state over a monarch.

However, it is unclear how the Scottish Government can pursue its ambition to create an independent Scotland with the current UK Government and a likely new Labour Government opposed to an agreed referendum, as happened in 2014 and the Supreme Court ruling last year that Holyrood has not got the power to hold a vote unilaterally.