"We won't be able to settle all areas in detail by the end of 2020," Maas told the RND newspaper network.

Britain will leave the European Union on Friday and Prime Minister Boris Johnson says 11 months is time enough to strike a "zero tariff, zero quota" trade deal. He has vowed — even though the option is there — not to extend the limbo period beyond 2020.

"A deal without tariffs and quotas sounds good but that's only one side of the equation", Maas said. "The other side is: No unfair subsidies and no social or environmental dumping."

Maas stressed that the EU and Germany still wanted to have close ties with Britain, adding: "It's not farewell - Britain is not going to suddenly swim away."

(Reporting by Michelle Martin; Editing by Madeline Chambers)