For months, Britain’s cabinet has been divided between those like Philip Hammond, the chancellor of the Exchequer, who want to prioritize the interests of the economy over control of immigration, and the hard-line supporters for Britain’s exit, or Brexit, who are eager to sever ties with the bloc without regard to the economic ramifications.

On Tuesday, Mr. Hammond seemed to emerge the victor in one battle, securing cabinet support for the soft transition from membership of the customs union. Introducing the plan, David Davis, Britain’s main Brexit negotiator, noted that other European Union nations, which export more goods to Britain than it sends back, have an interest in making it work.

Under the proposal, Britain would quit the customs union, but seek to join something almost identical for a period. During that time, it would want to be allowed to sign — but not put into effect — trade deals with other partners.

That stipulation — like everything else — has to be agreed upon with the other 27 European governments, which may oppose such a move. And experts say that countries like the United States or India would not be in a position to strike trade deals with Britain until they know more about its future economic relationship with the European Union.

In any event, the British plan was given a cool reception by European Union officials, who said there would be no negotiations on that point until “divorce” issues have been settled, like the exit bill London would have to pay and the rights European Union citizens in Britain would have. Hence, the talk about “fantasy” from Mr. Verhofstadt.