BRUSSELS (Reuters) - Britain’s new leaders should not expect to have access to the European Union’s single market while leaving the bloc and the duties of membership, Belgian Prime Minister Charles Michel said on Tuesday.

Belgium's Prime Minister Charles Michel talks to the media as he arrives at the EU Summit in Brussels, Belgium, June 28, 2016. REUTERS/Eric Vidal

“If we have a leader in the U.K. and they think they can use only the advantages of the EU without any solidarity it will not be possible,” Michel told Reuters on the sidelines of an EU summit in Brussels following last week’s Brexit referendum.

“We have to be realistic,” he said. “It’s true for the European Union, but also true for the leaders in the U.K.”

Michel and other EU leaders were being briefed by Prime Minister David Cameron over dinner about how Britain saw the way forward after the vote, which prompted his own resignation.

Cameron has left it to his successor, who may not be known until September or October, to activate a two-year timetable for negotiating Britain’s withdrawal. Frontrunning pro-Brexit candidate Boris Johnson has said Britain can retain many of the benefits of free trade with the other 27 while not being an EU member and subject to rules such as free migration in the bloc.

Staunch defenders of the European project, such as Belgium, fear giving such a degree of concession to London would lead to others demanding similar treatment and so unravel the bloc.

“You cannot send a message where it would be possible to be out of Europe, without all the inconvenience, and at the same time with all the advantages,” Michel said. “You can’t say, ‘I divorce you, but I’ll live with you for a few days a year’.”

Cameron’s refusal to trigger the withdrawal mechanism under Article 50 of the EU treaty, has worried EU leaders who say the uncertainty risks destabilizing the continent.

“It’s very important to have a clear situation as soon as possible,” Michel said. “I’m a little bit surprised that the leaders in U.K. and the leaders of the Brexit in the U.K. are saying they need more time.”

“The referendum was a risk but now there is a decision and we have to assume the consequences,” he added, saying British leaders faced difficulties holding the United Kingdom together.

British officials are concerned that the two-year deadline set under Article 50 for negotiating a divorce, without which Britain would simply be cut off from EU markets, is too tight.

Michel insisted that without the clock being set ticking there could be no negotiations with Britain. But, he said: “I think it’s possible in two years to have a complete agreement.”

Michel, who was among Cameron’s main opponents in talks in February to restrict immigration from the EU to Britain, said he wanted a mutually beneficial deal with London and did not want to see a near neighbor to remain in deep trouble.

“But I am paid to defend and to protect the interests of my country and of the European project,” he added.

Ahead of a first meeting on Wednesday of the 27 EU leaders without Britain to plot the Union’s way ahead, Michel said it was important to hold the rest together, but he wanted some states to be able to forge ahead faster in cooperation.

He insisted he was not pushing for a European federal super-state and did not see such a project as realistic.