The co-leaders of the Scottish Greens have rejected an invitation to a service of thanksgiving for the King in Edinburgh this week with one of them due to speak at an anti-monarchy rally.

Patrick Harvie and Lorna Slater – two of the most outspoken republican MSPs in Holyrood and Scottish Government ministers – announced their intentions on Tuesday.

The special service to mark the King’s coronation will take place at St Giles’ Cathedral on the Royal Mile on Wednesday, where he will be presented with the Honours of Scotland – the country’s crown jewels.

Mr Harvie will instead speak at a rally outside Holyrood organised by the anti-monarchy group Our Republic.

Ms Slater said: “In 21st century Scotland, the monarchy is nothing to celebrate.

“It is an out-of-date and undemocratic institution.

“How can we justify a system that allows one family to enjoy so much unearned wealth and privilege at a time when millions of people have so little?

“Scotland can be a modern and democratic republic with an elected and accountable head of state.

“I want every child in Scotland to know they live in a genuine democracy and that they can achieve the highest office, regardless of which family they come from.”

While Mr Harvie added: “There are many people in Scotland who regard the monarchy as a tiresome spectacle and a symbol of values we don’t hold.

“I will be proud to speak at the Our Republic rally and to stand with others who want to build a more democratic society where power and wealth belongs to the people rather than being passed down as an inheritance.

“That is just one reason why I support Scottish independence. It will give us the opportunity to ask the big questions about how we are ruled and to build a fairer and more equal society.”

But Scottish Tory constitution spokesman Donald Cameron said the decision was akin to “student politics”, and Mr Harvie’s choice to speak at the rally instead was “predictably infantile”.

“If he wants to ask big questions, he should start with how he conducts himself as a government minister,” he said.

“The Greens may have failed to deliver a deposit return scheme, but they can definitely recycle tedious anti-monarchy rants.

“As on so many issues, the extremist Greens are out of touch with the majority of Scots, who see the coronation and the King’s commitment to Scotland as something to celebrate.”