Spain and France may be projecting joy at the prospect of a U.K. homecoming, but officials are cautioning that unwinding Brexit will involve costs and sacrifices it’s not clear either side wants to bear.

New U.K. Prime Minister Andy Burnham touched off a flurry of speculation on Tuesday that he may campaign to reenter the E.U., before confirming he would discuss the prospect at an upcoming summit with the bloc’s leaders. Europe’s heavyweights quickly jumped on the opening.

“Welcome back,” French President Emmanuel Macron quipped in English, smiling while speaking alongside Spanish Prime Minister Pedro Sanchez. Spain, Sanchez added, would “open its arms” to a U.K. reunion.

The behind-the-scenes reality is less rosy, according to people familiar with the relationship, speaking anonymously to describe private talks. There is lingering concern in Brussels about British flip-flopping, given the country’s revolving-door prime ministers of late. And for the U.K., rejoining would also reopen debates over prior E.U. exemptions and deals that may no longer be available.

The wariness reflects the suspicion and hurt that remain 10 years after the U.K. voted to leave the E.U. The two sides frequently make stop-start progress on all kinds of negotiations — and that’s when talks don’t break down amid recriminations.

Still, E.U. officials have been pleased by Burnham’s new message, the people said, even as they caution that they’ll wait to see what action actually follows. Burnham said he would also raise with E.U. leaders the possibility of the U.K. rejoining the bloc’s single market or entering a customs union.

“The U.K. is a close and valued partner of the European Union,” Balazs Ujvari, a spokesperson for the European Commission, the E.U.’s executive arm, said in a statement on Wednesday. “It is for the U.K. government to set out how it wishes to develop its relationship with the E.U. going forward.”

Former Labour officials who worked under Keir Starmer, Burnham’s predecessor, expressed skepticism about a complete remarriage. They warned that the E.U. would likely impose significant costs on Britain to rejoin, adding that was one reason why Starmer’s team had been reluctant to pursue the option.

One said that when they previously talked informally to E.U. counterparts about the costs of rejoining, they were told there would need to be a renegotiation of a U.K. budget rebate agreed to under Margaret Thatcher. That could mean extra costs of roughly £5 billion ($6.6 billion) a year to return.

The person added that they didn’t think the E.U. would insist on Britain joining the Schengen Area, the E.U.’s passport-free travel zone, or adopting the euro currency. But accepting freedom of movement would be non-negotiable.

Another former Labour aide said that either rejoining or entering a customs union with the bloc would mean Britain would have to void the free trade agreements it had signed since Brexit, most notably with India.

For now, the two sides are expected to remain focused on more low-hanging fruit heading into the summit next month.

The gathering — which was postponed after Starmer resigned — will likely focus on three smaller elements: linking the E.U. and U.K. carbon markets, agreeing on food and agriculture trade and a youth mobility program for both travel and work.

The limited ambition reflects the headwinds still facing the E.U.-U.K. relationship, despite ties improving since a center-left Labour government took over in 2024.

The two sides have split over forthcoming “Made in Europe” legislation from Brussels, which would prioritize E.U. sources when public money and investment decisions are made. The U.K. has joined other allies like Japan and Switzerland to protest the planned rules given their close investment relationship.

Another point of tension is the E.U.’s flagship €150 billion defense loan program, which offers countries funding for military purchases. Talks for the U.K. to join the program fell apart last year, reducing the amount of money that could go to British firms.

Bloomberg also previously reported that the E.U. pushed back on U.K. efforts to attend key meetings.

Specifically, the U.K. expressed interest in joining committees fine-tuning regulations on farming and food standards, as well as the bloc’s carbon and electricity markets — all areas where London is trying to align its rules with the continent.

The commission told member states the U.K. had no right to such participation under its current arrangement, while several countries opposed giving the U.K. any involvement in E.U. decision making.

U.K. Treasury Minister James Murray was quick to manage expectations in an interview on Thursday. “This is not about leaping forward to one particular conclusion,” he told LBC radio. “This is about having an honest debate, putting out the options, seeing how people feel about them, and then trying to come to a consensus about what happens next.”

—With assistance from Jorge Valero, Alberto Nardelli, Kirsi Heikel, Suzanne Lynch, James Regan and Jacob Reid.

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