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.

"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."

Mr Juncker also reportedly said he would not seek a second term as European Commission president when his five-year term expires in 2019.

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 US president.