Oliver Robbins has been moved to 10 Downing Street from the Department for Exiting the European Union (DexEU) to take on a new "coordinating" role, which will see him work more closely with Prime Minister Theresa May.
"In order to strengthen cross government coordination of the next phase of negotiations with the European Union, the Prime Minister has appointed Oliver Robbins as her EU Adviser in the Cabinet Office, in addition to his role as EU Sherpa," a DexEU statement said.
"He will continue to lead the official-side UK team in the negotiations, working closely with the Secretary of State for Exiting the European Union, and coordinate relations with the European Commission and Member States," it noted.
However, the main reason behind the shift is being attributed to tensions between him and Brexit secretary David Davis.
The change at the top of the Brexit pecking order within government is also being seen as a way for May to take on greater control of the negotiations after days of rows over the issue within her own Cabinet.
The latest set of wrangles were triggered over the weekend with a 4,000-word article by UK foreign secretary Boris Johnson reviving his claims that the country's National Health Service (NHS) would be 350 million pounds a week richer as a result of Brexit.
While this figure has come under dispute since he first used it during the Vote Leave campaign in the lead up to the EU referendum last year, his decision to re-open the debate is being widely seen as a blatant leadership challenge to Theresa May by trying to take centre-stage within the Brexit debate.
"Once we have settled our accounts, we will take back control of roughly 350 million pounds per week. It would be a fine thing, as many of us have pointed out, if a lot of that money went on the NHS," he wrote in The Daily Telegraph.
The article, in which Johnson also said he opposed paying the EU to secure temporary access to the single market during a transitional phase after the UK's departure, divided Conservative party MPs with many claiming it undermined May's leadership ahead of a crucial EU speech scheduled for later this week in Florence, Italy.
Many are reportedly calling on May to sack her foreign secretary over this intervention.
While UK home secretary Amber Rudd accused her Cabinet colleague of being a Brexit "back-seat driver", defence minister Tobias Ellwood warned his party of growing discord with his tweet: "We are not witnessing our finest hour-at a testing time when poise, purpose and unity are called for.
"Debate should be forward looking on how to make most of life outside EU – not refighting referendum."
Meanwhile, a parallel row broke out between Johnson and the chair of the UK's Statistics Authority, David Norgrove, who wrote a letter to contest the minister's claims: "I am surprised and disappointed that you have chosen to repeat the figure of 350 million pounds per week, in connection with the amount that might be available for extra public spending when we leave the European Union."
The authority warned that the article "confused" the size of the UK's annual gross and net contributions to the EU's budget and also assumes that payments currently made to the UK by the EU, including for example for the support of agriculture and scientific research, will not be paid by the UK government when it leaves.
"It is a clear misuse of official statistics," he said.
Johnson's reply was equally harsh: "I must say that I was surprised and disappointed by your letter of today, since it was based on what appeared to be a wilful distortion of the text of my article.
"You say that I claim that there would be 350 million pound that 'might be available for extra public spending' when we leave the EU. This is a complete misrepresentation of what I said and I would like you to withdraw it."
The Opposition parties are having a field day with the ruling Conservatives’ internal chaos, with Liberal Democrat leader Vince Cable saying Johnson’s credibility had been "shot to pieces".
Keir Starmer, Labour’s shadow Brexit secretary, said it all smacked of "chaos".
"Moving key individuals at this critical time adds a whole new dimension to the government’s chaotic approach to Brexit. Deep divisions in the Cabinet and a complete lack of leadership are putting the national interest at risk," he said.