European Central Bank said Britain's financial industry, which employs 2.2 million people, would lose the right to serve clients in the EU unless the country signed up to its single market
German Chancellor Angela Merkel sought on Saturday to temper pressure from Paris, Brussels and her own government to force Britain into negotiating a quick divorce from the EU, despite warnings that hesitation will let populism take hold.
Eurosceptics in other member states applauded Britons' decision to leave the European Union in a referendum that sent shockwaves around the world, with far-right demands for a similar vote in Slovakia underlining the risk of a domino effect.
With the referendum decision finally made on Thursday and Prime Minister David Cameron having announced his resignation, European politicians and institutions felt free to shower demands on Britain over its future outside the world's largest trading bloc.
The European Central Bank said Britain's financial industry, which employs 2.2 million people, would lose the right to serve clients in the EU unless the country signed up to its single market - anathema to "Leave" campaigners, who are set to lead the next government in London.
Almost alone in continental Europe, Merkel tried to slow the rush to get Britain out of the EU door. Europe's most powerful leader made clear she would not press Cameron after he indicated Britain would not seek formal exit negotiations until October at least.
"Quite honestly, it should not take ages, that is true, but I would not fight now for a short time frame," Merkel told a news conference.
"The negotiations must take place in a business-like, good climate," she said. "Britain will remain a close partner, with which we are linked economically."
Others demand urgency
Britain's decision to leave the EU is the biggest blow since World War Two to the European project of forging greater unity. But Merkel appeared more conciliatory than others within her coalition government and elsewhere in Europe.
The chief executive of Britain's "Vote Leave" campaign called for informal talks before London notifies the EU it wants to leave under the Lisbon Treaty, which provides for two years of divorce proceedings.
But German Foreign Minister Frank-Walter Steinmeier, a member of Merkel's Social Democrat coalition partners, showed a greater sense of urgency.
"This process should get under way as soon as possible so that we are not left in limbo but rather can concentrate on the future of Europe," he said after hosting a meeting with his colleagues from the other five founding members of the EU - France, Italy, the Netherlands, Belgium and Luxembourg.
French Foreign Minister Jean-Marc Ayrault warned of the dangers of delay. "We have to give a new sense to Europe, otherwise populism will fill the gap," he said.
They followed European Commission President Jean-Claude Juncker, who said on Friday it made no sense to wait until October to negotiate the terms of a "Brexit".
European Council President Donald Tusk made a start by appointing Belgian diplomat Didier Seeuws to coordinate negotiations with Britain.
Britain's representative on the EU executive, Financial Services Commissioner Jonathan Hill, resigned on Saturday after campaigning against a British exit.
In Britain itself, divisions widened after the relatively close 52-48 percent vote.
More than 2.4 million Britons signed a petition on parliament's website, posted before the vote, calling for a second EU referendum if the outcome was close on a turnout of less than 75 percent - three points above Thursday's figure.
The petition will have to be considered for debate by lawmakers, but it has no legal force and its backers compare with the 17.4 million who voted "leave".
Tens of thousands are also set to pack into Trafalgar Square in the British capital on Tuesday to show "London stands with Europe", the Evening Standard newspaper reported.
The divisions also took their toll on the opposition Labour Party, whose leader, Jeremy Corbyn, sacked shadow foreign minister Hilary Benn on Sunday, media reported, after he said he would resist any attempt to oust him.
Corbyn has been criticised by some of Labour's elected lawmakers who say he did not campaign hard enough in support of EU membership.
Scotland's pro-EU first minister said she wanted to open negotiations directly with Brussels. The option of a second referendum on independence from the United Kingdom - after Scots rejected the idea two years ago - was "on the table", she said.