European Commission President Jean-Claude Juncker said he fears Britain will divide the European Union's 27 remaining members by making different promises to each country during its Brexit negotiations, Reuters reported.
"The other EU 27 don't know it yet, but the Brits know very well how they can tackle this," Juncker told Deutschlandfunk radio. "They could promise country A this, country B that and country C something else and the end game is that there is not a united European front."
Britain will by the end of March trigger formal divorce talks with the EU, a major test for the bloc which is struggling to have a grip on other challenges like keeping Greece in the euro zone, the refugee crisis and the election of Donald Trump as U.S. president.
To add to all of that, the Netherlands, France and Germany are holding general elections this year, in which populist anti-EU parties are expected to make strong showings.
"Now everyone is saying in relation to Trump and Brexit: 'Now is Europe's big chance. Now is the time to close ranks and march together,'" Juncker said in the radio interview which will be aired on Sunday.
"I wish it will be like this, but will it happen? I have some doubt. Because the Brits will manage without big effort to divide the remaining 27 member states."
His warning echoed remarks by German Chancellor Angela Merkel at an EU summit in Bratislava last year aimed at finding a way forward after Britain's vote to leave, that the bloc is in a critical situation.
Juncker said one area where the remaining 27 could improve cooperation was defense. Britain and France are the only EU countries with nuclear arsenals.
Juncker, who will host U.S. Vice President Mike Pence in Brussels next weekend, said a protectionist trade policy by the Trump administration would be an opportunity for the EU to forge new trade alliances.
"It would be a change that we have to use," Juncker said. "And we should not allow the Brits to pursue trade deals now with others because they are not allowed to do so."
He added that as long as Britain was in the bloc, the European Commission was in charge of negotiating trade deals.