Boris Johnson has appointed Lord Frost as a full member of his Cabinet, tasking the chief Brexit negotiator with a key role overseeing the future relationship with the European Union.

Downing Street said on Wednesday that the Conservative peer will become a minister of state in the Cabinet Office, reporting to the Prime Minister, from March 1.

He will also replace Michael Gove as chair of the UK-EU joint committee on the Withdrawal Agreement, a key role as Northern Ireland faces post-Brexit trade disruption.

And Lord Frost will be the UK’s chair of the Partnership Council, which will try to resolve disputes arising from the trade deal with Brussels.

The Prime Minister earlier ditched plans to make his ally Lord Frost the National Security Adviser days before he was due to take up the role.

Next month the unelected peer will be a Cabinet minister, expected to co-ordinate relations with the EU and its 27 member states and work on post-Brexit regulatory changes.

Lord Frost said: “I am hugely honoured to have been appointed minister to take forward our relationship with the EU after Brexit.”

He added that he would be standing “on the shoulders of giants”, particularly of Mr Gove, “who did an extraordinary job for this country in talks” with Brussels.

Mr Gove said it was a “great appointment”, adding that there is “no-one better to take forward our post-Brexit relationship with the EU”.

But Labour’s shadow international trade secretary Emily Thornberry said: “So we’ve finally got one minister taking a grip of the problems with our post-Brexit trading relationships with Europe.

“Someone who has never been elected by anyone in this country, and won’t be accountable in the House of Commons to any of us who have.”

Last week, Lord Frost blamed the severely strained tensions with the European Union on Brussels struggling to accept a “genuinely independent actor in their neighbourhood”.

He told MPs that the EU needed to adopt a “different spirit” in order to ease the “more than bumpy” relationship since the end of the post-Brexit transition period on December 31.

A statement from No 10 said: “The Queen has been pleased to approve the appointment of Lord Frost CMG as a minister of state in the Cabinet Office.

“Lord Frost will be a full member of Cabinet. His appointment will take effect from March 1 2021.”

When previously reversing the decision to appoint Lord Frost security adviser, the Prime Minister’s official spokesman said he had been appointed representative for Brexit and International Policy and head of a new International Policy Unit in No 10.

The Prime Minister’s official spokesman said: “He will lead the UK’s institutional and strategic relationship with the EU and he will help drive through changes to maximise the opportunities that flow from the deal we reached with the EU.”

Lord Frost, a former career diplomat who went on to be the chief executive of the Scotch Whisky Association, served as a special adviser to Mr Johnson when he was foreign secretary.

After succeeding Theresa May as Prime Minister, Mr Johnson appointed the Brexit true believer to lead negotiations with Brussels, opposite the EU’s Michael Barnier.

Lord Frost is an ally of Mr Johnson’s controversial former chief adviser, Dominic Cummings, but did not follow him out of No 10 following his dramatic departure amid a bitter power struggle.