EU chief Charles Michel urged Britain on Wednesday to decide what kind of a future it wants for itself rather than trying to win an advantage in negotiations with Brussels.
"You can't have the butter, the money from the butter and the milkmaid's smile," the president of the European Council said, a French maxim that means: "You can't have your cake and eat it."
Britain's Prime Minister Boris Johnson has described himself as a "cakeist" and he has accused Brussels of thwarting negotiations on a free trade deal by insisting the UK submit to EU rules.
But Michel said Britain would have to decide what it wants, warning: "It's a matter of the integrity of our Single Market. A question of fair competition.
"Our UK friends say they want an ambitious and close relationship. We welcome this, because we want the same," said Michel, whose Council represents the leaders of EU member states.
"But the UK wants access to our Single Market, while at the same time, being able to diverge from our standards and regulations, when it suits them," he complained, in an address to the European Parliament.
"In fact, the United Kingdom now has an important choice to make about its own future," he said.
"It's not about choosing a negotiating tactic. It's about choosing the model of society and the model of economy for their own future."
Michel urged Britain to commit to high standards of business regulation in any agreement and to withdraw the UK's internal markets bill, which if passed would violate the Brexit withdrawal agreement.
"We want to keep access to UK waters for our fishermen," he warned, "exactly like the UK wants to keep access to our huge and diversified markets for its companies.
"Do our British friends want to regulate state aid?" he demanded. "And do they want to maintain high standards in health, food safety, and climate, in close relationship with Europe?"
"If so, why not commit to them in our future agreement?" he asked.