Angus Robertson has labelled the UK as “archaic” and warned that the lack of a written constitution is failing “to protect the key values” held by Scots.

The Edinburgh MSP has stressed that the UK constitutional arrangements are putting key Scottish values and fundamental rights at risk of erosion.

The Constitution Secretary’s intervention comes after the Scottish Government published a paper outlining nine occasions it is claimed the UK Government has used Westminster’s sovereignty to undermine the Scottish Parliament without consent.

Mr Robertson has highlighted the erosion of the Human Rights Act as more evidence for his government's allegation another fundamental pillar of Scottish society is under attack by the UK Government.

The Cabinet Secretary has also branded the UK a “constitutional outlier” for the lack of a written constitution that is the normal setup in most modern democracies and in all EU member states.

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During the SNP leadership campaign, Humza Yousaf pointed to rights being embedded in a written constitution if Scotland becomes an independent country.

On Monday, the First Minister is set to launch the Scottish Government’s fourth independence paper which will focus on an independent Scotland drawing up a written constitution. The Constitution Secretary has backed up that call, warning that the UK is a “constitutional outlier” without a comprehensive written document.

Mr Robertson said: “The UK’s constitutional arrangements are archaic and fail to protect the key values held by those who live in Scotland. “The basic principles that underpin our society should be decided by the people they affect, not by any parliament or government of the day.

“The current constitutional setup faced by Scotland puts the sovereignty of the Westminster Parliament above all else – which has left fundamental aspects to our life, such as Holyrood’s democratic will and even the Human Rights Act, open to attack by the current government.”

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He added: “The UK is a constitutional outlier, with almost all modern democracies having a written constitution enshrined in law.

“All 27 EU member states have a written constitution, and it’s time Scotland did too.

“In step with other progressive nations, an independent Scotland will have a written constitution to enhance citizen’s rights, designed and agreed on by the people it serves.

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“A better, fairer and more equal Scotland is possible through independence – that’s the vision the First Minister will share on Monday.”

Last month, Scottish Secretary Alister Jack insisted his blocking of the gender recognition reforms was “not an attack on devolution”.

The UK Government has tabled plans to replace the Human Rights Act with a Bill of Rights, which it says would “help prevent trivial human rights claims from wasting judges' time".

Tory ministers also insist the overhaul would make it clear UK courts do not always need to follow the decisions of European courts.

But the Joint Committee on Human Rights said the proposals restrict certain protections "the government finds inconvenient".