Brussels is on edge, but it has no intention of going back to the Brexit drawing board.

Chief Brexit negotiator Michel Barnier told a meeting of EU27 ambassadors Friday morning that whatever political "difficulties" Theresa May is experiencing in London, the bloc has a "duty" to stand firm on its key Brexit red lines, according to EU diplomats present.

For her part, May is standing firm on the deal in the face of a gale of criticism and is intent on pushing the deal to a vote in the House of Commons. But if political opponents in her own party succeed in forcing her to seek a better deal, there is no sign that any of the EU27 red lines will change.

We cannot "compromise" or engage in "cherry-picking" or "bargaining," Barnier told ambassadors, referring to requests to reopen the draft deal that was agreed by the British Cabinet on Wednesday. He added that he expects "difficult negotiations" ahead.

Barnier also expressed a desire to help the British government in its efforts to ratify the text in a vote of MPs. And he said that there could be room for movement on the EU side in specific areas, such as enhanced cooperation on phytosanitary regulations and so-called technical barriers to trade. It is a moment not for triumphalism, he said, but for "encouragement."

“All eyes are on London. We see there are some turbulences" — EU diplomat

The chief negotiator's presentation at the more than two-hour meeting reflects a dilemma for Brussels. While EU countries want to help May get the deal through parliament, there is a reluctance at such a late stage to radically unpick the agreement — despite threats to May's leadership and a series of ministerial resignations over the deal.

Diplomats say that some tweaks might still be possible if they could make the difference between the deal succeeding or crashing, but the kind of radical overhaul proposed by Brexiteers such as former Brexit Secretary David Davis is simply not on the table. There is "no question" of that, German Chancellor Angela Merkel said Thursday.

"If we renegotiate something it could be on very small details," said a senior EU diplomat "[but] it will not be on the main issues."

"Europeans are not scared, but very cautious, and everybody hopes the deal will be approved," he added, saying that the first major challenge will be the tight timescale to consider the details of the deal before a hastily arranged EU leaders' summit on November 25.

"Some of us will need to consult our MPs on the text, and make the necessary democratic deliberations in our countries," the diplomat added.

“All eyes are on London,” said another EU diplomat. “We see there are some turbulences.” Asked about the mood in Brussels, the diplomat said: “It’s a feeling of relief that at least there’s a text on the table.” A third diplomat added: “Everyone is committed to getting the ball over the line."

In any case, as Barnier said Wednesday, EU capitals feel that they have already given significant ground in the final stages of the talks. And not everyone is happy with all aspects of the final deal.

“We had to accept compromises," said the second diplomat. “There are some points that also make some EU members uncomfortable.”

The diplomat cited the EU's acceptance of an all-U.K. customs backstop — as an insurance measure to prevent a hard border in Northern Ireland — and the decision to kick negotiations about fisheries access into the transition period that will immediately follow Brexit day in March next year. "It’s not clear, and it will affect millions of jobs," said the senior EU diplomat. "There’s nothing precise."

Barnier was briefing ambassadors on the state of ongoing talks about the political declaration — the document that will accompany the 585-page Withdrawal Agreement. Only a cursory seven-page outline of that was published on Wednesday evening and the chief negotiator indicated that several issues are still in play.

"Any regulatory gap is a serious issue" — Senior diplomat

On security matters including participation in EU agencies such as Europol and Eurojust he said, according to two EU diplomats, that the U.K. does still "not accept" the full ramifications of not being an EU member country. But Barnier added that both sides share the aim of close cooperation. And on mechanisms to ensure there is a level playing field between British and EU businesses after Brexit, EU ambassadors expressed reservations in the discussion following Barnier's briefing.

"Any regulatory gap is a serious issue," said the senior diplomat, adding that the text "isn’t clear" on environmental and social measures. "The consequences are important because it could enhance any regulatory gap on major issues." One country's representative is also "worried" that the text offers too much to the U.K. on services.

Despite the desire not to contribute to political instability in London, not all EU politicians are adopting a softly softly approach. France's economy minister, Bruno Le Maire, said on Friday that Brexit is leading Britain into “a nightmare” and called on “lying and irresponsible” Brexiteers to abandon their project, or face economic meltdown.

“The British politicians, who have argued for Brexit, now have a choice between reneging on their absurd political promise or an economic disaster of which the British people will be the first victim,” he said.

His more cautious colleagues may be hoping that the people he is referring to are too preoccupied to notice.

David Herszenhorn contributed reporting.