In London these days, most developments in Europe are seen through the prism of Brexit. The result of the French presidential election has therefore boiled down to this: Will Emmanuel Macron be good or bad for the U.K. in its imminent negotiations over leaving the European Union?

The first response from Paris to London is likely to be ‘This isn’t about you.’ The president-elect has other fish to fry. He must first work to build a majority in the National Assembly in next month’s elections. Then his first international priority will likely be to rebuild France’s relationship with Germany.

On the face of it, Mr. Macron will be a hard-liner over the negotiations. During his campaign, he described himself as a “hard Brexiter.” Calling Brexit a crime at one point, he said Britain couldn’t enjoy EU rights as a nonmember or the EU would fall apart.
Despite this, there was relief in London that Mr. Macron won. Prime Minister Theresa May warmly congratulated him, describing France as “one of our closest allies.”

That wasn’t just politeness. The real worry in Whitehall was a victory for the fiercely anti-EU Marine Le Pen that would have pitched the bloc into so much turmoil that constructive divorce negotiations would have become nigh impossible.

But is Mr. Macron just—as Maurice Chevalier once said about old age—better than the alternative?

After Mr. Macron’s victory on Sunday, his chief economic adviser, Jean Pisani-Ferry, said the U.K. and France had “a mutual interest in keeping prosperity” and maintaining their very important security and defense relationship.

But he said that while Mr. Macron had no wish to punish Britain, the president-elect believed “even today that Europe is part of the solution to the problems we are facing. He’s not the sort of man who would implicitly agree to a dismemberment of the EU.”

This suggests Mr. Macron won’t want to create incentives to leave the bloc and therefore won’t veer from the standard EU line that the U.K. can’t have a more advantageous relationship with the EU outside the bloc than it does inside.

Politics at home in France suggests an even tougher attitude. With the traditional political parties there in disarray, the main opposition over Mr. Macron’s five-year term is likely to come from Ms. Le Pen’s ranks. His incentive in the negotiations may thus be to play up difficulties to demonstrate that leaving the bloc is a very bad idea.

In an interview this week with the BBC, Mr. Pisani-Ferry also said France and the U.K. had “divergent interests in some aspects of the negotiations.” In an email exchange afterward, Mr. Pisani-Ferry declined to be drawn on what those “divergent interests” were.

“We understand that London is very focused on the Brexit negotiations but although we fully recognize the significance of the matter, we have many other urgent issues to deal with,” he said.

One obvious area of divergence stands out: financial services. German officials, while conceding they know little directly of Mr. Macron’s intentions, believe he is likely to adopt the departing French government’s hard line on Brexit, particularly on limiting the ability of Britain’s financial-services industry to do business with EU and eurozone clients.

Several Berlin officials said this week that Paris was eager to encourage City of London businesses to move operations and jobs to the continent. Berlin, however, is skeptical that Paris, Frankfurt or Luxembourg can match the competence and critical mass of the City. By restricting the access of EU companies to the City, they fear, the 27 remaining member states could end up raising the cost of doing business in Europe.

This concern is consistent with Germany’s wish to strike a balance between softening the economic and trade impact of Brexit and deterring any country tempted to follow the U.K.’s example.

But the chief Brexit concern for German officials now is hardly Mr. Macron, but Mrs. May. They worry she might be underestimating the technical and legal complexity of separating Britain from the EU, which they think could prove a bigger obstacle to an orderly Brexit than the political differences. In the German view, London should be worried less about Paris and more about clarifying what it needs to do at home.