John McTernan is a former speechwriter for ex-British Prime Minister Tony Blair and ex-communications director to former Australian Prime Minister Julia Gillard. The opinions expressed in this commentary are his.

(CNN) A man you've never heard of resigns from a job you didn't know existed. How worried should you be?

If you care about the UK getting a good deal from Brussels after it leaves the European Union , then quite worried. Especially if that man is Sir Ivan Rogers and the post is the UK's permanent representative to the European Union, or more colloquially, the British ambassador to the EU.

The contents of the resignation email that Rogers sent to his colleagues -- which has been published by various British media outlets -- suggests that the UK government is still some way from having a solid negotiating position for when it leaves the EU. The fact that the email was sent from a man of his stature , more damningly, betrays how unprepared the government is for a fistfight with Brussels when the time comes for those negotiations.

In my experience, ambassadors fall into two categories -- timeservers and class acts. Sir Ivan was the latter.

When I first met Sir Ivan, he was Tony Blair's principal private secretary: the civil service head of the prime minister's office. He was -- and is -- sharp, witty, fast-thinking, intellectually challenging and hard-working. He was an ideal senior civil servant, and one with the rare gift of being able to move seamlessly between prime ministers.

Having worked for Blair, he was later able to be former PM David Cameron's adviser on Europe in No. 10 and then Cameron's appointment as ambassador to the EU.

In this job, he has excelled. First, he delivered nearly all that Cameron wanted from a pre-referendum deal. He then moved on to leading the Brexit agenda for Britain's new prime minister, Theresa May.

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So, what has gone wrong? Why has he suddenly -- and surprisingly -- resigned? The clue is in the key section of his lengthy resignation email to his staff:

"Serious multilateral negotiating experience is in short supply in Whitehall, and that is not the case in the Commission or in the Council.

"The government will only achieve the best for the country if it harnesses the best experience we have - a large proportion of which is concentrated in UKREP - and negotiates resolutely.

"Senior ministers, who will decide on our positions, issue by issue, also need from you detailed, unvarnished - even where this is uncomfortable - and nuanced understanding of the views, interests and incentives of the other 27.

"The structure of the UK's negotiating team and the allocation of roles and responsibilities to support that team, needs rapid resolution."

Blunt and to the point. Theresa May and Brexit Secretary David Davis need unvarnished and uncomfortable advice. And they need to resource properly the machine that can deliver this advice.

Sir Ivan did not suffer fools gladly. That is the best kind of person to work with if you are a politician who wants to know the facts -- the full facts -- so that you can craft a full and effective strategy.

But the current UK government seems intent on centralizing power and only hearing good news. For Sir Ivan Rogers, the politics of Brexit -- and the future of his country -- was too important to play along with this.

In his email he carefully puts the word Brexit in quotation marks, preferring to use the word exit about the UK's future. In similar fashion he talks about "invoking" Article 50 rather than "triggering" it.

The more passive tone will have infuriated No. 10, because it reflects a horrible truth: that the UK is in a weak negotiating position. No amount of bluster from the PM or David Davis can change that. What they can change -- and what they have changed -- is who leads for the UK in negotiations. But by forcing Rogers out they have revealed how weak the current No. 10 operation is. As he says:

"We do not yet know what the government will set as negotiating objectives for the UK's relationship with the EU after exit."

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That is undoubtedly a question he has repeatedly internally. Rather than answer it, No. 10 has made it clear that he is not needed. The broader signal is clear too: civil servants have to toe the government line and hide uncomfortable facts and challenging questions from ministers.

That is never a good idea. Intellectual challenge leads to good policy and -- in the end -- good policy is good politics. When you face a negotiation which will determine the UK's prosperity for the coming decades, it is a dereliction of duty and leadership for No. 10 to want to close down internal debate.

Negotiating Brexit successfully with 27 different countries requires skills and deep relationships. One of the central relationships -- between the government and the permanent civil service -- has just been trashed and it will ultimately be to Britain's cost when it comes to dealing with Brussels.