LONDON — For the U.K., French President Emmanuel Macron’s visit this week is a chance to try out a new diplomatic approach.

According to U.K. diplomats, Britain intends to use summits like the get-together at Sandhurst — the British Army’s main military academy in Berkshire, southwest of London — to retain its influence on the Continent after it leaves the formal diplomatic infrastructure of the EU.

The British strategy is to rebuild long-neglected bilateral relations to maintain influence in Europe. The trouble for the U.K. is that, when it comes to EU countries, bilateral relations can only go so far. Membership in the bloc places limits on what agreements national governments can strike with countries outside the EU, especially in crucial realms like economics and trade.

That has left the Brits scrambling to find areas for fruitful cooperation.

Macron and a coterie of ministers will cross the Channel Thursday for a one-day Franco-British summit that will shape the future of Europe’s most important military relationship — one of the areas that remains clearly out of Brussels’ jurisdiction.

“Seen from France, this comes at a point of weakness for the U.K." — Jonathan Eyal, associate director at RUSI

But as the two sides prepare to meet, the contrasts are stark. For Macron, the summit is another chance to showcase France’s growing clout on the European stage as he tries to reshape his country as the Continent’s one essential power after Brexit — with both economic and political influence to rival Germany and the added ability to project military force outside Europe.

For U.K. Prime Minister Theresa May, weakened by her botched general election gambit last year and Britain’s loss of influence in Brussels, the challenge is simply to stay relevant, according to diplomats and foreign policy analysts.

How the summit pans out for each side will be a major indication of how Europe’s two remaining military powers see their relationship unfolding after Brexit and how successful — if at all — the U.K. will be in remaining a player in European affairs after 2019.

The military treaty between the U.K. and Poland, signed in Warsaw in December, was the first indication of this new strategy of bilateralism.

One U.K. official briefed on the strategy said this week’s summit will go beyond defense and look at a whole range of other issues, from security cooperation to cyber threats, economic ties and climate challenges.

“On these areas we want to put in place a road map of where we want to work together going forward,” the U.K. official said. “We want to make a lot of the relationship and will invest a lot in it.”

According to officials briefed on the matter, announcements are expected on defence and security cooperation, extending the scope of the Franco-British Combined Joint Expeditionary Force, new initiatives on Calais and greater cultural exchanges.

The Conservative chairman of the foreign affairs select committee, Tom Tugendhat, said bilateral relations with France needed to go beyond the areas covered while the U.K. was a member of the EU. “We must talk to the French not just about the military alliance that matters to both of us, but our economic and social links too,” he said.

“These bilateral connections with our EU neighbors will mean investing more in our embassies in Europe to ensure we don’t lose influence in our region,” said Tugendhat. “But we can’t strip resources from our wider network if ‘Global Britain’ is to be more than a slogan. That means more money for diplomacy to shape the world and ensure we continue to help write the rules that have seen us prosper and others grow.”

In a statement released ahead of the summit, May explicitly acknowledged the summit was a chance to show Britain’s commitment to Europe post Brexit. She said: “Our friendship has always gone far beyond defense and security, and the scope of today’s discussions represents its broad and unique nature.”

“What is clear from the discussions we will have today is that a strong relationship between our two countries is in the U.K., France and Europe’s interests, both now and into the future,” she added.

In Paris, however, the gathering 30 miles outside London is an opportunity to test what France believes is its newfound dominance in the relationship, caused in large part by Brexit, according to diplomatic insiders.

“Seen from France, this comes at a point of weakness for the U.K.” said Jonathan Eyal, associate director at RUSI, the Royal United Services Institute for Defence and Security Studies, a London think tank. “There is a feeling in Paris that they can extract more concessions from the British today — it’s no longer seen as a meeting of equals.”

The most eye-catching concession is likely to be a commitment by the U.K. to contribute more to the French-led mission in Mali, where Britain’s lack of involvement has long irked Paris. As part of a series of defense and security deals set to be announced, Britain will send three Chinook helicopters to support French troops operating in the Sahel region. The U.K.’s Department for International Development will also spend an additional £50 million in aid to the region to lighten the load on Paris. In return France will commit troops to the U.K.-led battlegroup in Estonia in 2019.

Bilateral cooperation on intelligence will also deepen, an ambition marked by a meeting, in advance of the summit, of the heads of the U.K.’s three and France’s two leading intelligence agencies. The meeting, at an undisclosed location, is the first time the five intelligence chiefs have met all together. A U.K. government spokesperson said that “recent terrorist attacks across Europe” had underlined “the scale of the cross-border challenge” the two countries face.

The U.K. is also expected to make new commitments on infrastructure at the port of Calais, where thousands of migrants trying to get to the U.K. set up camp waiting for an opportunity to cross over. Macron has vowed to “rebalance” the Le Touquet agreement, which effectively moved the U.K. border to Calais to help stop the crossings.

Macron’s stance is a climb-down from the hard-line demands he had presented when he was still France’s economy minister two years ago, and reiterated during his presidential campaign, that the Le Touquet accord be “renegotiated” and the border controls moved back to U.K. territory. A French presidential aide said France is now just looking for what he called “improvements” to the deal.

“The U.K. is trying to recreate a relationship which went out of fashion in the 1960s" — Jonathan Eyal

The fundamental problem for the U.K. is that beyond its military power — which diminishes with each round of defense cuts — there’s not much that can be included in bilateral discussions that EU countries have not contracted out to Brussels.

And on the French side, the desire for vibrant bilateral ties with the U.K. cannot yet include the economic and trade dimensions. Those are currently under EU chief Brexit negotiator Michel Barnier’s remit and will continued to be governed by EU rules after Brexit.

Earlier this week, Macron insisted he would be firm in defending France’s interests on, for example, fisheries, but that is a question he must first discuss with Barnier and France’s EU partners as they debate the Brexit envoy’s mandate for the next rounds of negotiations.

This week’s summit “is really the first hesitant attempt to forge a bilateral relationship with France,” said Eyal. “For the U.K. the problem is what will be the substantive content, beyond military cooperation, in these bilateral relationships after Brexit?”

“The U.K. is trying to recreate a relationship which went out of fashion in the 1960s,” he added. “It’s now so counterintuitive to modern diplomats — both sides will be grasping in the dark to make this work.”

Pierre Briançon and Charlie Cooper contributed reporting.