Prime Minister Boris Johnson on Friday kept the door open to more Brexit talks but insisted Britain was ready to slam it shut unless the EU offers "fundamental change" in its tactics, as the clock ticks down to a potentially messy divorce.

Johnson was responding after the European Union at summit talks Thursday demanded he give ground on key stumbling blocks while also proposing a fresh round of talks next week in London.

The summit outcome appeared to rule out a comprehensive, Canada-style free trade agreement between the EU and Britain, Johnson said, accusing the 27-nation bloc of failing "to negotiate seriously" in recent months.

"They want the continued ability to control our legislative freedom, our fisheries, in a way that is obviously unacceptable to an independent country," he said in a broadcast interview.

He said that "unless there is some fundamental change of approach" from the EU, Britain's favoured approach for an all-encompassing deal was out. "And so with high hearts and complete confidence we will prepare to embrace the alternative," Johnson said.

He said Britain should "get ready" to operate on stripped-down World Trade Organization rules from January akin to Australia's relationship with the EU.

"And we can do it, because we always knew that there would be change on January 1 whatever type of relationship we had," he said, pointing to sector-by-sector arrangements in areas such as social security, aviation and nuclear cooperation. "And we will prosper mightily as an independent free-trading nation, controlling our own borders, our fisheries, and setting our own laws."

More talks?

The British pound slid below $1.29 in response to Johnson's comments but pushed the London stock market up 1.3 percent, as the weak pound lifts multinationals earning in dollars.

Johnson had set the EU summit as a deadline for a deal, but is under pressure after fresh warnings that British companies are nowhere near ready for the consequences of a cliff-edge divorce when a post-Brexit transition periods ends on December 31.

Britain wants to reassert sovereignty over its waters and refuse EU legal oversight over any deal, insisting it wants an overarching trade deal of the kind the EU adopted with Canada in 2017. Brussels in turn stresses that Britain's economy is far more integrated with the EU's than Canada's, and that its single market must be protected from British backsliding.

At their Brussels summit, EU leaders demanded Britain compromise on fair trade rules to unblock the stalled post-Brexit talks. Chief negotiator Michel Barnier also proposed more meetings in London next week and the EU confirmed it would be in the British capital to intensify negotiations from Monday.

Irish prime minister Micheal Martin said EU leaders had given Barnier "the necessary flexibility to continue with the negotiations... to ensure a comprehensive fair and free trade deal". "That's how we would like to see things evolve from now and in the future... to bring this to a conclusion," he told reporters in Brussels.

The insistence of France and other northern EU fishing nations on maintaining access to British waters has been another key stumbling block in the talks so far.