In a letter to the Scottish and Welsh governments, he said Cardiff and Edinburgh should keep the UK involved in all contacts decentralized governments have with EU institutions. Lord Frost said they should keep the “UK government informed” of the “content” of all meetings of senior officials and ministers with the European Commission and other EU institutions.
He said it was because the UK needed to conduct its “international affairs” effectively with Brussels and made it clear that he did not want secret contacts.
Scottish government ministers led by the SNP have already written to the European Commission and have had regular talks with officials in Brussels amid difficult trade talks between Lord Frost and Michel Barnier.
But Lord Frost said in the letter that he expected decentralized administrations to “support” the UK government’s position on contacts with the European Commission and other EU bodies.
He continued in his letter: “Now that our trade and cooperation agreement with the EU has been fully ratified, I would like to explain how the government intends to work with you to ensure its effective implementation.
“I truly intend to do this on a constructive and mutually beneficial basis.”
The letter was also sent to the chief ministers of Jersey, Guernsey and the Isle of Man alongside the executive of Northern Ireland.
Lord Frost has also invited Scottish External Affairs Minister Angus Robertson and Wales Minister for the Constitution Mick Antoniw to a summit next month.
Mr Frost said his officials would contact Scottish and Welsh officials ahead of the first Joint Partnership Council meeting with the EU in early June.
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The Partnership Council will implement and monitor the free trade agreement and has not met so far.
Lord Frost said he would like to meet to “discuss UK approach” ahead of the meeting.
But the Cabinet minister concluded by saying that he has overall control over “UK relations with the EU”.
Donald Cameron MSP, spokesman for the Scottish Conservative Constitution and External Affairs, said: “During the UK government’s negotiations with the European Union, the SNP government attempted to undermine discussions on various issues, despite the the fact that the British government was clearly leading the negotiations on behalf of the four countries of origin.
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“This remains the case as we continue our trade relations outside the European Union.
“The best chance for a positive arrangement will come from the SNP’s commitment to work closely with the UK government going forward in any discussions with the European Union.”
Michael Russell, who retired as Constitution and External Affairs Secretary in April, has had regular meetings with his EU counterparts and with ambassadors from member countries.
Mr Russell said the Scottish government “deeply regrets the fact and the modalities of the UK’s exit from the European Union”.
Nicola Sturgeon, Prime Minister of Scotland, recently pleaded with Eurocrats saying Scotland is being dragged out of the EU against its will.
Ms Sturgeon made the call in a desperate message sent to newspapers across the continent where she said she hoped Scotland could ‘soon join you as an equal partner as we face together the opportunities and challenges of the future”.
But tonight the Scottish government said it was “in everyone’s interest for the EU and the UK to have as close a relationship as possible”.
A spokesperson added: “The Scots overwhelmingly support staying in the EU.
“The Scottish Government will continue to be a voice for mutually beneficial cooperation and of course we will continue to advance the interests of Scotland at all times.”
A Welsh government spokesperson added: ‘We have received the letter and will respond in due course.’
It comes after the Cabinet Office minister revealed to the House of Lords this week that none of the 24 bodies set up under the trade deal have so far met, but “most” should have met before the summer.
Independent MP the Earl of Kinnoull, who chairs the Lords European Affairs Committee, pointed out that the trade deal would have six months in June and said: “Hearing the lack of activity is disheartening.”
He argued that governance of the deal was important “to get the parties to iron out the problems.”
Lord Frost said: “I agree that it is extremely important that all bodies established under the Trade and Cooperation Agreement come together and work effectively.”
While he insisted that there had been “no lack of activity” between him and his EU counterpart, he agreed that “it will produce stability when these committees function properly”.