LONDON — Theresa May began the summer reiterating that "Brexit means Brexit." She will return to work on Wednesday under pressure to explain what British withdrawal will look like.

In her absence, a chasm of expectation has opened up between increasingly hardline expectations in Westminster, where Euroskeptics believe their plan for a short, sharp Brexit is well-received by team Theresa, and established opinion in Brussels and other European capitals about what is politically acceptable and legally possible.

Despite an impressively assured start in the job that has seen the Tory lead over Labour widen, May’s task navigating this yawning gap remains daunting.

The boldest option on the table — and that favored by the hardliners — is for an immediate snap Brexit, dubbed “unilateral continuity” by Tory MPs. Under this proposal the U.K. simply informs Brussels that it has left the EU and does not impose trade tariffs unless the rest of the EU does so first.

The radical plan, which veteran Euroskeptics believe is being studied seriously in Whitehall, would see May trigger Article 50 and then pass an act of parliament to annul the 1972 European Communities Act, unilaterally taking the U.K. out of the EU.

Brussels insiders dismiss the plan, insisting that it is illegal and would see the EU taking Britain to court.

Most Euroskeptic hardliners accept that such a snap Brexit is an "option B" scenario and would prefer a negotiated free trade agreement, but they are cheered that the more radical option is even being considered.

“I’m telling you, they are listening,” one leading hardliner said. “It is a grown-up government. I genuinely believe they do not yet have a position and are taking soundings. Don’t forget, we have been working on this stuff for years.”

Buried in these assurances, however, is a clear message for May: Brexit has to mean a hard Brexit.

Post-referendum Tories

The new prime minister's early moves in Number 10 won her breathing space with the Tory right.

Euroskeptic MPs welcomed her insistence that she would deliver Brexit and impose controls on free movement. They were also delighted with appointments of senior Leave campaigners such as Foreign Secretary Boris Johnson, International Trade Secretary Liam Fox and Brexit Secretary David Davis.

To further calm potentially troublesome MPs, Number 10 and the Department for Brexit quietly opened up channels with leading Euroskeptics over the summer.

In conversations with Conservative MPs, not one believed it was democratically acceptable for Britain to stay in the single market if it meant maintaining freedom of movement.

“The dynamics have completely changed on Euroskepticism now," one influential pro-Brexit MP said: "It’s the government’s policy to leave. It’s going to take ages for everybody to get used to the idea that we are no longer angry, isolated Euroskeptics.”

Asked why they had faith in May, one leading Brexiteer explained: “Two things, Nick Timothy, the chief of staff, is for exit and the relevant people are persuaded that that isn’t going to change. [And] the prime minister is evidently determined to have control on who can live and work in the U.K., so I just don’t think there’s going to be a problem.”

The mood music has shifted among pro-EU Tories too. In conversations with more than a dozen Conservative MPs, ministers and government aides not one believed it was democratically acceptable for Britain to stay in the single market if it meant maintaining freedom of movement.

“We don’t want a halfway house," said one fervently pro-EU Conservative minister. "It will just feed the machine without delivering us any say. I can’t see how we are going to settle for something that doesn’t settle freedom of movement. It has to be a bilateral free-trade agreement with the EU.”

The minister also insisted that pro-EU Tory MPs would not give the government the same kind of problems that committed Euroskeptics had in the past now the European boil had been lanced.

A senior trade official in Brussels said that one of the most serious dangers of Britain leaving the EU would be reputational damage.

“The whole whipping operation [which enforces party discipline among MPs] has been predicated on the idea of the ‘bastards’ [Euroskeptic rebels] but that has gone.

“The problems will be far more issue-based — they will come and go. It will be fiendishly difficult to pin down where the opposition will come from. But these are not existential, ideological battles. We’re all for Brexit now."

He said there was an acceptance that the new deal had to be “bold.”

“Remember we are operating with the constraints of what the British people told us,” he said. “We are constrained by the sheer fact of the referendum.”

Hardline Conservative MP John Redwood put it more bluntly: “There is absolutely no way we can stay in [the single market]. There is no doubt about it.”

Legal headaches

Trade lawyers, on the other hand, are unimpressed with the snap Brexit plan.

A senior trade official in Brussels said that one of the most serious dangers of Britain simply extracting itself from the EU would be reputational damage. If London broke its international treaty obligations, that would jeopardize its chances of striking deals with the U.S. and China, which would see it as an untrustworthy partner, he said.

Alberto Alemanno, a law professor at HEC in Paris, agreed that a unilateral Brexit would be illegal. He added that it would also weaken Britain's hand in negotiations, which will have to tie up thousands of loose ends ranging from pensions to healthcare.

"The 'hard Brexit' hypothesis would run foul of EU law and the obligations that still bind the U.K. to the other 27 member states," he said. "Leaving the EU without respecting the exit procedure under Article 50 would immediately endanger the new U.K.-EU relationship, thus weakening the U.K. negotiating position."

German MEP Bernd Lange, chief of the European Parliament’s international trade committee, said a snap Brexit was simply “not possible.” He added: “As long as you are a member under EU law, you are a member.”

With a warning to the U.K. government, he added: “If they really proceeded with this, we would take them to court and eventually take counter-measures ... One should not expect the EU would just let such a thing happen.”

“I don’t see them really pursuing such a plan. They just don’t have the resources at the moment, starting with the very obvious lack of negotiators for concluding new trade deals. Now running off harum-scarum sounds very illogical to me.”

Trade experts cite a range of other complications — including the status of trade deals already agreed between the EU and third countries. Leading British companies would be immediately dumped out of agreements with countries ranging from South Africa and Colombia, to South Korea and Ukraine. Companies would face immediate tariffs and would lose any safeguards offered by the legal framework of those deals.

EU officials are also clear that, under EU law, the U.K. would automatically face basic external tariffs as soon as it dropped out of the single market.

EU officials are also clear that, under EU law, the U.K. would automatically face basic external tariffs as soon as it dropped out of the single market. This means Britain will face steep barriers to trade in sectors such as agriculture and cars. As a far smaller trading power than the EU 27, a tit-for-tat trade battle over goods would be much more painful for Britain than for the rest of the Continent, Brussels believes.

"A simple cost-benefit analysis suggests the U.K. should not venture down the hard Brexit road," Alemanno argued.

"The renegotiation between the 27 and the U.K. is somehow inescapable unless the U.K. wants to cut its trade relations with all countries," he said.

EU leaders have been clear from the beginning that access to the single market, such as that enjoyed by Switzerland, comes hand in hand with free movement. Both France and Germany will hold elections in 2017, opening up the possibility that the political temperature could change during the course of negotiations.

Political gymnastics

Downing Street has privately played down the need for a confrontational Brexit.

“There is a certain sentiment [elsewhere in Europe] that maybe the Commission was not flexible enough, that in some way [David] Cameron’s diagnosis of the problems with the EU was correct and that to some it’s been a bit of a wake-up call,” a source said.

But will May be able to keep Euroskeptics onside without a hard Brexit?

May will have to get any deal with Brussels through the House of Commons, where she is operating with a wafer-thin working majority of just 17. With the same majority, Cameron was forced to abandon proposals to change the way English schools are run. May has to unpick 40 years of European integration.

“All it takes is half a dozen malcontents on her own backbenches and she’s scuppered,” one senior Conservative Party source said, reflecting a sentiment shared by many in Westminster. “Party management is by far the most difficult job of being prime minister. This is her biggest challenge. Just think of those she’s already p--sed off sitting on the backbenches.”

May’s team is quick to reject the notion that the government risks being held to ransom by 30-40 Tory hardliners who will not accept anything less than full and immediate sovereignty. “That assumes the Labour Party is not going to agree with the government’s plans,” the source said. “She [May] wants to do something that is good for the whole country.”

In a bid to manage party expectations, May quickly established much tighter central control of the government machine. “They are calling everything in,” one special adviser explained. “It’s what I would do. They don’t want any major f--k ups in the first few months that will define everything afterward.”

A government minister, speaking on condition of anonymity, agreed. “She is taking a direct involvement at a much earlier stage,” he said. “It is very Thatcheresque. Number 10 will be considerably better informed than it was before. The previous regime would only really get involved in the later stages.”

May plans to dominate the Brexit process from the beginning.

Every policy is now funneled through May’s powerful joint chiefs of staff Nick Timothy and Fiona Hill, prompting concern that the tubes of government could quickly become blocked.

May plans to dominate the Brexit process from the beginning. Johnson, Fox and Davis will all sit on a special Brexit cabinet committee chaired by the prime minister, which will be the ultimate decision-making authority on the U.K.'s exit.

One Euroskeptic MP, broadly content with May’s intentions, admitted there could be problems if things dragged on. “You can rely on some to get angry about almost anything, so there will be some anger if it’s not quick.”

Tory-supporting media is already agitated. Thursday’s Daily Mail editorial fired an early warning: “Brexit opens up great opportunities for a self-governing Britain,” it said. “Mrs. May should hurry up and seize them.”

A government minister added: “The issue is the capacity now and the timetable and how quickly this can all be done.”

Downing Street insists the plan remains to begin the formal process of leaving early in the New Year.

Whatever the timing, the British appear to be heading out the door — and slamming it shut behind them.