One person who will take a lot more persuasion is Michel Barnier, the European Union’s negotiator, who on Friday said that “in the Brexit negotiations there are still too many questions and too few answers.”
The new plan, scheduled to be published as a white paper next week, will be judged by Mr. Barnier both on practicalities and against the European Union’s red lines.
Mrs. May’s preferred customs plan is seen by most officials in Brussels as unworkable. More generally, the European Union has insisted all along that Britain will not gain access to the single market without accepting its core principles like the free movement of people, which Brexiteers abhor.
Mrs. May’s plans present other difficulties, for example, by differentiating between manufactured goods — which would be under Europe’s rule book — and services, which would have a more distant relationship.
Distinguishing between goods and services will become increasingly hard, for example, in the auto market as vehicles, which already sometimes come with loans or insurance deals, become increasingly reliant on digital technology.
Other thorny issues include the extent to which British manufacturers would be subject to Europe’s state aid rules (to prevent unfair competition), the jurisdiction of the European Court of Justice — another institution loathed by Brexiteers — and European labor and environmental laws.
Friday’s declaration suggested that Britain would accept European antitrust rules but would want to set up new bodies to resolve trade disputes “founded on the principle that the court of one party cannot resolve disputes between the two.”
Brussels has so far insisted that Britain must either opt to stay in the single market fully — accepting free movement — or settle for a much more minimalist free trade deal like that with Canada. Mrs. May has always argued for something in between and has, in recent days, visited both the Dutch prime minister, Mark Rutte, and the German chancellor, Angela Merkel, to try to ensure that her plans are — if not exactly welcomed then — at least not dismissed out of hand.