'Alister Jack should resign if he can't stand up to James Cleverly'

The guidance, which has prompted new tensions between London and Edinburgh, tells UK diplomats that meetings between overseas ministers and the Scottish Government should be arranged through the Foreign, Commonwealth and Development Office.

Mr Cleverly called for a “strengthened approach” to Scottish ministerial visits ensuring officials from the UK Government are present during meetings with foreign governments saying that there were concerns the Scottish Government was promoting "separatism" during meetings with overseas officials and ministers and undermining UK Government policy.

READ MORE: Boris Johnson ally Lord Frost calls for downgrading of Holyrood

Days after the Foreign Secretary's letter emerged Tory peer Lord Frost called for Holyrood's powers to be stripped back.

As Scotland Office minister Mr McLeish steered the Scotland Act 1998 through the Commons working under the then Scottish Secretary Donald Dewar in the late 1990s. The legislation determined the original powers of the Scottish Parliament.

Former First Minister Henry McLeish.   Photo Gordon Terris, The Herald

He said the devolution settlement allowed Scottish minsters to carry out work in international affair, for instance to promote the country's trade, culture, tourism and education, though issues such as signing international treaties and decisions to go to war were reserved to Westminster.

He said Mr Cleverly's letter was a "mistake" and suggested he did not understand the devolution settlement which he and Mr Dewar had helped create.

"This letter [by James Cleverly] is part of a wider assault on devolution," said the former First Minister.

READ MORE: Robertson warns Foreign Secretary new rules will damage Scotland

"It's the contempt, the disrespect, but it's also about political control and coercion. This Tory government does not recognise the spirit of devolution and to me Cleverly was ill advised to write this.

"He has not got constitutional powers to do so. Donald Dewar and I knew that Scotland can become involved in international relations so my advice to the Foreign Secretary is to withdraw the letter because it has no meaning and secondly if he doesn't withdraw it then I would advise the Scottish Government and the parliament to ignore the sentiments in it."

He added: "The other point is this the Secretary of State has a role here. The Secretary of State is supposed to represent Scotland's interests in the UK Conservative Government.

"He is not doing that and what he looks like is a willing ally of Westminster in trying to undermine devolution. My advice to him is to acknowledge that Cleverly's letter was a mistake. And if he doesn't then the Secretary of State for Scotland should consider his position.

READ MORE: Ministers to consider new justice changes in wake of SNP finance probe

"Scotland's Secretary of State role is to look after the interests of Scotland, not look after the interests of the Tory party."

Earlier this month Angus Robertson, the Cabinet Secretary on External Relations, demanded the Foreign Secretary withdraw the guidance issued in the letter accusing him of penning a “misleading” document which damages Scotland’s interests.

Mr McLeish was Scotland's second First Minister from 2000 to 2001 and an early advocate of the country's work overseas.

He pointed to Holyrood taking part from its early days in Tartan Day celebrations in the United States and that he established a presence of a first secretary for Scotland in the UK's embassy in Washington.

Mr McLeish visited Washington DC in April 2001 and met with the US President George W Bush for 40 minutes in the White House's Oval Office.

"Donald Dewar and I had the view there was nothing stopping Scotland from operating on the world stage," the former First Minister told The Herald.

"We had historical relations with the United States because of the diaspora and in 1998 the US Senate passed a motion declaring Tartan Day every year on April 6.

"I was determined we would start to impact on the global stage in a modest way."

He went on to say that following the UK's withdrawal from the European Union it was even more important for the Scottish Government to enhance Scotland's relations with other countries across the world.

"This is not about independence, this is about Scotland, the nation, being able to build links with Europe for a variety of reasons - for education, business, tourism, culture, our diaspora, climate change, science and technology.

"We have an absolute democratic right to be doing all of that. Post Brexit we have to make sure that our links with Europe are not lost.

"And my contention is is that the Scottish Government and the Scottish Parliament should be doing more in Europe and internationally generally to try and make up for the the UK Government losing respect the world."

Mr McLeish said he would like to see the Scottish Government open more hubs in European cities as well as other countries and also called for SNP ministers to establish a "Council on Overseas Relations" allowing the country to deepen its international expertise.

In addition he also called for more work to be done to forge links between Scotland and its millions strong overseas diaspora.

An UK Government spokeswoman said: “Any suggestion that the UK Government is suppressing Scotland’s voice from being heard internationally is absurd. The 800 staff based at FCDO’s joint HQ in East Kilbride are at the very heart of shaping and delivering UK foreign policy.

“The Scottish Government’s Constitution and External Affairs Secretary, Angus Robertson, recently praised the FCDO at the Scottish Affairs Committee for its strong record of supporting the devolved governments. Promoting every area of the UK is part of our DNA.

“The Foreign Secretary’s guidance will not change the UK Government’s commitment to working collaboratively with each of the devolved governments and their ministers in the delivery of devolved policy objectives, while ensuring reserved competences are fully respected.”