LONDON: Britain on Friday formally told the European Union that it would not extend the post-Brexit transition, raising the alarming prospect of a disorderly split in six months.

London and Brussels have made very little progress in agreeing a new trade deal for when Britain leaves the EU's single market and customs union on December 31.

But Prime Minister Boris Johnson rose to power last year on a pledge to "get Brexit done", with the issue roiling UK politics - and consuming time in Brussels - ever since Britons voted to leave the bloc by a narrow margin in 2016.

His government had until July 1 to ask for more time, which Brussels was willing to give. "That's it," senior minister Michael Gove told British television after finishing online talks with his EU counterparts.

"We are leaving the European Union on December 31."

In Brussels, EU commissioner Maros Sefcovic said Gove "couldn't be clearer".

"I take this as a definite conclusion of this discussion," Sefcovic said.