Welcome to the momma-cussing, rap-battling, “are you disrespecting my family” phase of the Brexit talks. Though the official negotiations have yet to begin, the insults are already flying. It cannot be long before a senior EU figure says of Theresa May: “Your mother was a hamster and your father smelled of elderberries.”

The warm-up has been steady. In March, Jean-Claude Juncker, the European commission president, said with understated menace that the UK’s decision to leave the European Union was a “choice they will regret one day”. Last month, Guy Verhofstadt, the European parliament’s chief Brexit negotiator, dismissed our imminent departure as “a catfight in the Conservative party that got out of hand”.

Now, following a tense dinner on Wednesday for EU leaders at No 10, the heat has been turned up. In this weekend’s Sunday Times, Juncker is reported to have told Angela Merkel that May is “in a different galaxy”. An unnamed diplomatic source informed the paper that the prime minister’s views on the UK’s financial settlement with Brussels “border on the delusional”. Another accused her of conjuring demands “from a parallel reality”.

Well, what did you expect? Instant accord, fist-bumps across the Channel, Beethoven’s Ode to Joy followed by Pomp and Circumstance? This will be, first and foremost, a diplomatic mud fight in which both sides have much at stake. The better angels of their nature may be on holiday for a while.

On the BBC’s Andrew Marr Show, the prime minister said more than once that “at times these negotiations are going to be tough”. David Davis, the Brexit secretary, has conceded repeatedly that “the dynamics of the negotiations will go hot and cold, from time to time.” In private, those involved in the talks – and they are many – sound even more daunted by the task ahead, as well they might.

In Brussels this weekend, the 27 other EU member states spent just four minutes endorsing the EU’s guidelines for the management of Brexit. They are not lacking in provocation.

According to the blueprint, “no agreement between the EU and the United Kingdom may apply to the territory of Gibraltar without the agreement between the Kingdom of Spain and the United Kingdom.”

The plan raises the prospect of “flexible and imaginative solutions” in “the island of Ireland” – a clear signal that Northern Ireland would be welcomed back into the fold quickly if it opted to unite with the Republic. While the UK wants parallel talks about its exit and its future relationship with Brussels, the 27 are no less adamant that “the first phase of negotiations” must address the rights of EU citizens living here and our outstanding financial liabilities.

Yet the appearance of impasse, stand-off and potentially insuperable difficulty is often an essential part of any serious arbitration. The diplomatic choreography requires the transaction to be presented as a zero-sum game, when it may be no such thing.

Brexit secretary David Davis. Photograph: Andy Rain/EPA

Read the EU guidelines carefully, and watch the wriggle room open up between the sentences and phrases. For instance: the communique requires only that “sufficient progress” be made on the terms of exit before negotiations “proceed to the next phase”.

This is entirely consistent with what Davis told the Commons select committee for exiting the European Union in March: “If there is a technical issue that holds up the actual detail of resolution, what I will try to do – and I think I will succeed – is get an exchange of letters that makes absolutely plain what we think the outcomes will be and should be … so we get both sides of the negotiation to agree that.”

In other words: if he and Michel Barnier, the EU’s chief negotiator, cannot settle an exact financial figure or the precise legal status of EU citizens in post-Brexit UK, they may yet agree statements of principle, and proceed to other issues. In the prelude to the Good Friday agreement, the negotiators made ample use of what David Trimble, the Ulster Unionist leader, liked to call “constructive ambiguity”. Expect plenty of that in the Brexit talks.

The guidelines also make explicit and distinct mention of “potential issues arising from the withdrawal in other areas of cooperation, including judicial cooperation, law enforcement and security” and the EU’s readiness to “establish partnerships” in these areas.

A prime minister with a working majority of 17 is vulnerable to rebellion by a handful of her own MPs

When May wrote in her article 50 letter in March that “in security terms, a failure to reach agreement would mean our cooperation in the fight against crime and terrorism would be weakened”, she was pilloried for blackmailing the EU. The language of this weekend’s plan suggests that, for all the bluster to the contrary, the message has been received loud and clear. The 27 know that failure to reach a deal will have consequences beyond trade and commercial relations.

The risks in all this are vertiginously high, which is precisely why May needs, as she told Marr, “a strong hand” when she goes to the table. Whatever else the Tory manifesto includes, the core purpose of this general election is – overtly – to grant her the freedom to manoeuvre that she requires in order to negotiate effectively.

Verhofstadt recently said in the Observer: “For those sitting around the table in Brussels, [the scale of May’s majority] is an irrelevance.” This is self-evident nonsense. If our soon-to-be-ex-partners know that she lacks political authority at home, they will take her to the cleaners.

A prime minister with a working majority of 17 is vulnerable to rebellion by a handful of her own MPs. What she seeks on 8 June is not, as is so often claimed, a mandate for hard Brexit, but the ability – should she so choose – to tell the hard Brexiteers to shove off.

Only this way can May manage the nuance, complexities and trade-offs that the talks are bound to involve. As Amber Rudd, the home secretary, said on the day the election was called, a larger majority would permit the prime minister “to arrive at potential compromises within the EU”.

None of which liberates her – or the rest of us – from the gamble that lies ahead. This election is only the first of the battles that she faces, and by no means the toughest. But it is often said that only an idiot fights a war on two fronts. Whatever else the prime minister may be, an idiot she is not.