In this photo illustration, the European Union and the U.K. flag sit together in Knutsford, United Kingdom, March 17, 2016. Getty Images

Britain would become a minor trading post with no more significance on the world stage than the island of Guernsey if it votes to leave the European Union in a referendum next week, France’s economy minister was quoted as saying Saturday.

In an interview with French newspaper Le Monde, Emmanuel Macron said the EU would also have to send “a very firm message and timetable” to Britain if its voters backed quitting the EU, known as Brexit, on Thursday.

“In the interests of the EU, we can’t leave any margin of ambiguity or let too much time go by,” Macron was quoted as saying. “You’re either in or you’re out.”

“Leaving the EU would mean the ‘Guernseyfication’ of the U.K., which would then be a little country on the world scale. It would isolate itself and become a trading post and arbitration place at Europe’s border.”

Guernsey is a tiny island in the stretch of sea between Britain and France.

The International Monetary Fund has said a vote to quit the EU could leave Britain’s economy more than 5 percent smaller by 2019 than if it stays in the 28-nation club.

Opinion polls this week suggested the “Leave” camp was ahead of the “Remain” side ahead of the June 23 vote. Campaigning was suspended after the slaying of British lawmaker Jo Cox on Thursday.

Britain’s partners are stepping up warnings that if it votes to leave, banks and financial firms based in London could lose their money-spinning “passports” to EU markets.

“If the U.K. wants a commercial access treaty to the European single market, the British must contribute to the European budget like the Norwegians and the Swiss do. If London doesn’t want that, then it must be a total exit,” Macron warned.

The minister said the referendum, whatever the outcome, would force the EU to work at avoiding a possible “contamination” effect in other countries that could be tempted to leave the bloc.