LONDON (AP) — British Foreign Secretary Boris Johnson is offering Britons an unrealistic and unachievable vision of the U.K.'s future outside the European Union, Dutch Finance Minister Jeroen Dijsselbloem has said.

It's the latest sign that Britain's effort to woo EU leaders before formal exit negotiations is meeting with skepticism.

Dijsselbloem — who also heads the Eurogroup of 19 countries that use the euro currency — told the BBC that Johnson "is offering to the British people options that are really not available."

Johnson has been touring European Union capitals as Britain prepares to start formal exit talks with the 28-nation bloc.

British officials have been reluctant to provide details of what they hope to get from negotiations.

But Johnson was quoted by a Czech newspaper Hospodarske Noviny as saying the U.K. would likely have to leave the EU customs union, while retaining access to the bloc's single market in goods and services.

The customs union and the single market are both pillars of the EU's model of tariff-free trade within the bloc of 500 million people.

Dijsselbloem said Johnson "is saying things that are intellectually impossible, politically unavailable."

"To say, 'We could be inside the internal market, keep full access to the internal market, but be outside the customs union' — this is just impossible, it doesn't exist," Dijsselbloem told the BBC's "Newsnight" program.

"The U.K. will be outside the internal market and there will be some hindrances," he said. "The full free movement within the internal market can only be available if the U.K. also accepts the other freedoms of Europe, including migration within Europe."

Immigration was a major factor for many Britons who voted to leave the EU, and British officials insist they will end the free movement of people from the bloc into Britain — though few details have been provided.

On Tuesday the British government strongly rejected a report by a consultant for Deloitte claiming it had no coherent plan for Brexit.