Almost 18 months after Britons voted to quit the European Union, that question has not even been discussed by members of Prime Minister Theresa May’s cabinet, who are due to hold their first meeting on the subject soon.

The issue is so divisive within the Conservative government, however, that there are signs they will fudge the issue for a few more weeks by uniting around a request for an outcome that is almost certainly unachievable — a “Canada plus plus plus” deal.

Mrs. May has promised to take Britain out of the European Union’s customs union and single market, and is determined to restrict the right of citizens of countries in the bloc to live and work in Britain, and to reject a continuing role for the European Court of Justice — an institution Brexit enthusiasts loathe. That being the case, she has ruled out the option of copying Norway, which is part of the single market (but not of the customs union), and which respects both free movement and the court.

Under the “Canada plus plus plus” deal proffered by Britain’s chief Brexit negotiator, David Davis, the country would negotiate a free-trade agreement with the European Union, but with a much deeper set of agreements than Canada has.

That implies keeping close ties with the bloc but rejecting two of its pillars — the free movement of workers and the role of the European Court of Justice in adjudicating disputes. In this, experts say, Britain is once again barking up the wrong tree, in that European negotiators would never agree to such a deal because it would, in effect, reward Britain for leaving the bloc.

“The European Union is going to make it ever clearer there is a binary choice between Norway and Canada,” Mr. Menon said, “and that, in the case of Canada, you can forget the ‘plus plus plus.’”

Even agreements on nontrade issues, like data protection rules and security cooperation, might run into trouble because of Britain’s rejection of the European Court of Justice as an adjudicator, Mr. Menon said.