HELSINKI — The Finnish EU presidency on Thursday demanded Britain deliver a written proposal by the end of September on leaving the EU or face a no-deal Brexit, an ultimatum London immediately rejected.

The clock is ticking down on Britain's departure from the European Union, currently set for Oct. 31, but it appears increasingly likely it will crash out without any agreement.

A spokesman for Finnish Prime Minister Antti Rinne told AFP that Britain must deliver a written plan for a solution to the stalemate.

It is "a view of prime minister Rinne that the UK must come up with a written proposal by the end of this month," the spokesman said in a statement.

But Britain rejected the Finnish demand. "We will table formal written solutions when we are ready, not according to an artificial deadline, and when the EU is clear that it will engage constructively on them," a spokesman for the government of Prime Minister Boris Johnson said.

The Finnish deadline comes a day after Rinne met French President Emmanuel Macron in Paris, where he said the EU is unlikely to grant an extension to the current Oct. 31 exit date, and thus avoid a no-deal exit, unless London proposes concrete measures.

"Neither Finland, nor I, nor the other 26 member states have much enthusiasm for an extension unless there is a sensible solution in sight for the future," said Rinne, whose country currently holds the rotating presidency of the EU.

The current draft deal agreed with Brussels by Johnson's predecessor Theresa May was rejected three times by British MPs, largely because of its so-called "backstop" plan to keep open the border between British Northern Ireland and EU member Ireland.

But the EU has accused London of failing to come up with any concrete alternatives.

The British government spokesman said however that London has submitted "a series of confidential technical non-papers" to the EU, setting out Britain's ideas for an alternative to the customs backstop on the Irish border.

Technical "non-papers" are documents used in negotiations that do not represent a formal position.

However a spokeswoman for the EU Commission, Mina Andreeva, refused to call the papers an official written proposal.

"There are papers for now, until we have looked at them in detail, I will not characterize them beyond being papers," she told reporters in Brussels.

Britain's Brexit Minister Stephen Barclay confirmed he will meet the EU's chief negotiator Michel Barnier in Brussels on Friday, adding that talks with the bloc will now be stepped up.

"The prime minister returned from talks with President (Jean-Claude) Juncker in Luxembourg on Monday with assurances that negotiations will intensify," Barclay said in a speech in Madrid.

That trip to Luxembourg ended in humiliation for Johnson when he avoided what was meant to be a joint press conference with his counterpart Xavier Bettel, put off by a small anti-Brexit protest nearby.

On Thursday, a French diplomatic source told AFP that "time is running out" to reach a Brexit accord, warning that it will not be possible to negotiate "directly" at the next European Council meeting in mid-October.

The 28 EU leaders are due to meet on Oct. 17 and 18 in Brussels, less than two weeks ahead of the scheduled Brexit date of Oct. 31.

Britons narrowly voted in a 2016 referendum to leave the EU after almost half a century of membership, but the issue has left parliament and the country bitterly divided.

According to a European source, the Brexit timetable will also be discussed at a meeting between Johnson and Juncker on the margins of the UN General Assembly in New York next week.

Meanwhile, a case before Britain's Supreme Court to determine whether Johnson's controversial five-week suspension of parliament was unlawful began its third and final day.

Judges will rule on appeals against two conflicting lower court decisions, after Scotland's highest civil court found the suspension was unlawful, but the High Court in England said it was not a matter for judges to intervene in.— AFP