Brussels, in its conclusions on Brexit, is demanding a future relationship that “will have to be based on a balance of rights and obligations and ensure a level playing field.” That is Brussels-speak for British regulations and rules that do not diverge too far from Europe’s.

But if Mr. Johnson wants a free hand to make trade deals with the United States and other countries and to position Britain as more of a low-tax, light-regulation economy, Brussels will demand a tougher set of trade restrictions, unwilling to have a large competitor so close with significantly more favorable conditions for business and finance.

European leaders have agreed that the negotiations will be led by Michel Barnier, who also led the Brexit withdrawal negotiations and knows the issues well.

Ursula von der Leyen, the president of the European Commission, the bloc’s executive arm, said on Friday that Brussels would be ready to begin talks on Feb. 1, and that its goals were “zero tariffs, zero quotas, zero dumping.”

Eleven months would be a short time in which to finish a deal, she said, “but this is what we work for.” The talks “will be step by step but in an attitude that says we want to be good neighbors,” she added.

Mr. Johnson may favor a hard deadline, but that will put Britain, which will soon be negotiating from outside rather than inside the European Union, into a weaker position, argued Fabian Zuleeg, head of the European Policy Center, a research institution based in Brussels. The risk is that a quick trade negotiation, considered almost a contradiction in terms by trade experts, could fail, bringing Britain and Brussels back to the prospect of a “no deal” Brexit.

Many British businesspeople — and presumably some of the new Conservative Party members of Parliament from the industrial north of England — will want to be able to trade with Brussels with as little friction and paperwork as possible. That would mean closer alignment to the European Union than harder-line Brexiters advocate.