PARIS (Reuters) - French President Francois Hollande warned on Wednesday that if Britons voted to leave the European Union it would be an irreversible decision that could seriously jeopardize Britain’s prized access to the bloc’s single market.

French President Francois Hollande attends a military ceremony at the Hotel des Invalides in Paris, France, June 21, 2016. REUTERS/Jacky Naegelen

Amid a flurry of contacts between EU capitals to prepare for the consequences of Thursday’s referendum, Hollande said he would visit Berlin next week to prepare joint initiatives to relaunch Europe, whatever the outcome of the British vote.

“If the choice is to leave the EU ... that would be irreversible,” Hollande said. “No is no, there is no middle ground and we’ll have to draw all the consequences.”

The economic consequences of the vote are key to the outcome of the referendum, with access to the bloc’s single market for trade in goods and services a major issue.

Hollande, in his starkest warning to date on the consequences of Brexit, said: “There would be a very serious risk of Britain losing its access to the single market and everything that goes with the European economic area. Everyone needs to be well aware of this.”

While Norway is part of the single market via a trade deal it has with the EU, fellow non-EU member Switzerland only has access to parts of the single market.

European Commission President Jean-Claude Juncker added his own warning, saying there would be no re-negotiation of a package of measures that EU governments agreed with London in February aimed at keeping Britain in the 28-nation bloc.

Hollande’s call to relaunch Europe, Brexit or no, was echoed by both Slovak Prime Minister Robert Fico, who met the French leader in Paris on Wednesday, and by Polish Prime Minister Beata Szydlo during a visit to Berlin.

“We hope very much that the British want to remain in the EU. But irrespective of the result, our position is clear: the European Union should develop further,” Szydlo told a joint news conference with German Chancellor Angela Merkel in Berlin.

Hollande, who also met Swedish Prime Minister Stefan Lofven on Wednesday and spoke by phone with European Council President Donald Tusk and Dutch Prime Minister Mark Rutte, said there would probably be more summits of EU leaders than the one already scheduled for June 28..

“We’ll have to take initiatives to bring hope back for European people. Today, doubts are creeping in everywhere, populism, nationalism are taking over,” French Foreign Minister Jean-Marc Ayrault told parliament.

Far-right party leader Marine Le Pen, who according to opinion polls could top the first round of the 2017 French presidential election but then lose the run-off, has been pressing for France to hold its own referendum on EU membership.

“France has a thousand more reasons to leave the EU than Britain,” she told TF1 television late on Monday, referring to French membership of the euro currency and Schengen border-free area. “I want a referendum in France. All EU countries should have a referendum.”

British Prime Minister David Cameron and his euroskeptic opponents made final pitches for wavering voters on Wednesday on the referendum, with the outcome still too close to call.