European leaders toughened their stance Tuesday against British efforts to leave the European Union amid political chaos in London and other capitals, as E.U. officials gathered in Brussels for the first time since Britons’ shocking vote last week to break from the union.

Seeking to prevent a further crackup of their 28-nation bloc, nervous heads of government are trying to discourage other countries from following Britain’s example, telling London that it cannot preserve access to the world’s largest consumer market if it does not also accept the exact obligation that British voters seemed to reject: open borders. Some leading British exit campaigners already appeared to rein in ambitions for the split.

The pressure increased amid mounting confusion about just what the British exit campaigners planned to demand, and domestic political turmoil only appeared to emphasize the lack of clarity. European leaders said the best deal they could offer would resemble Norway’s. A non-E.U. member, that country has to submit to most E.U. rules and regulations in exchange for free access to the bloc’s rich markets. But Norway allows free movement of labor with the E.U., which would be a bitter disappointment for the British voters who just rejected E.U. membership. 

London cannot “cherry-pick” from the benefits of the E.U. without accepting its basic strictures, German Chancellor Angela Merkel said ahead of the dinner meeting in Brussels with British Prime Minister David Cameron and other E.U. leaders. In a pre-summit meeting with similarly aligned center-right leaders, she was caustic about Cameron’s handling of his nation’s relationship with the E.U., according to one official who was briefed on the discussions. 

After the United Kingdom voted to leave the E.U. in an historic referendum, voters were surprised that some of the rhetoric used to sway the vote to "Leave" was being walked back. (Jason Aldag, Max Bearak/The Washington Post)

“Those who want free access to the European domestic market will have to accept the basic European freedoms and the other rules and duties which are linked to it,” Merkel told the German Parliament. “This applies to Great Britain just like to everyone else. Free access to the domestic market is granted to those who accept the four basic European freedoms — of people, of goods, of services, of capital.” 

After the dinner of quail salad and veal, she added that she saw no possibility of reversing the decision. “This is not a time for wishful thinking,” she said. Leaders plan to meet Wednesday, without Cameron, to discuss their bargaining strategy.

Or, more succinctly: “Marriage or divorce, but nothing in between,” said Luxembourg’s prime minister, Xavier Bettel. 

With the future leadership of Cameron’s Conservative Party uncertain and Labour Party leader Jeremy Corbyn losing a Tuesday confidence vote amid dissatisfaction with his stewardship of the campaign to remain in the E.U., some proponents of the British exit dialed back their divorce demands. One contradiction inside Britain’s political establishment is that a majority of Parliament did not favor Brexit, leaving the leaders who must negotiate a divorce out of step with the majority of Britons who voted for the exit door in last Thursday’s referendum. 

World and U.S. markets and the pound rebounded Tuesday after tumbling since the surprise exit vote, suggesting that economic pandemonium may have eased — at least for the moment. Investors may also be betting that less will change in the relationship between Britain and the E.U. than they had initially feared. 

After the dinner Tuesday, Cameron suggested a vision for a divorce that appeared to preserve the status quo as much as possible, except for formal membership, but he said any concrete plans are likely to be left to his successor. The delay until September has annoyed E.U. leaders looking for a rapid withdrawal to avoid further chaos. 

“Britain should seek, and Europe should seek, the closest possible relations,” Cameron said, as he noted that he was probably taking part in his final conclave of European leaders. “We have a huge amount in common with each other.” 

He said he regretted losing the referendum but not having called it.

President Obama, who strongly sided with the pro-E.U. side in Britain, also has taken a cool-eyed view of the long-term impact of the decision, although he has acknowledged the messy financial and political fallout from the vote. U.S. diplomats have sought to play therapist to the seething Europeans, pushing for a calm approach to the crisis that would minimize the security and trade disruptions. 

But Europe, too, is split, as leaders seek to bar their own Euroskeptic movements from swelling in power after the referendum. Dutch voters in April rejected an E.U. deal with Ukraine, for example, leaving Dutch Prime Minister Mark Rutte trapped between the need for concessions from E.U. leaders and his desire not to derail the trade agreement.

Europe’s hard-line stance could come as a shock to British voters, who opted to exit the 28-member bloc on the basis of a “leave” campaign that had argued that Britain would continue to enjoy an advantaged trading relationship with Europe without having to abide by the continent’s free-movement rules. But since the vote, the pro-Brexit camp has splintered, with some continuing to press for an answer to immigration while others seem to quietly acknowledge that meaningful change is probably out of reach. 

The split reflects the awkward alliance that fueled the “out” campaign: On one side are libertarian free-marketers who want out of the E.U. in order to cut Brussels bureaucracy but who have no fundamental objection to immigration from Europe. On the other are cultural conservatives who dislike the way immigration has changed Britain and want it to stop. 

Leading Brexit campaigner Boris Johnson, the former mayor of London, falls into the former category.

After arguing for months that the country needed to “take back control” of its immigration system, he barely mentioned the issue in an op-ed in Monday’s Daily Telegraph. Instead, he emphasized the need to forge “a new and better relationship with the EU — based on free trade and partnership.” 

Johnson, who is considered a leading candidate to succeed Cameron as prime minister, has been conspicuously quiet since the result was announced Friday. Many of his fellow pro-Brexit leaders have also gone to ground. 

Their silence has unnerved ­anti-immigration firebrands such as Nigel Farage, who made a triumphant tour Tuesday of the press area in the building where the E.U. leaders were sitting down to dinner. 

“I’m a little bit nervous in the last 24 hours, because I’ve seen some figures on the ‘leave’ side who appear to be backsliding,” Farage said. 

Opposition to immigration may have been a focus for Brexit voters. But it does not appear to be motivating the handful of Conservative politicians likely to vie for Cameron’s job, none of whom have made an immigration crackdown a core issue. 

The muddle coming from London led some E.U. leaders to suggest — not without some schadenfreude — that they have little to discuss with Britain until the political establishment decides whether it wants a full split from the E.U. 

“The British people were quite clear on this,” said E.U. foreign policy chief Federica Mogherini. “But we are receiving contradictory messages from, to use an understatement, a rather confused political scene in London.”

Witte reported from London. Anthony Faiola in Berlin and Brian Murphy in Washington contributed to this report.