Updated 5.20pm

The European Union's two top officials handling troublesome Brexit talks warned Wednesday the risk of a no-deal exit looms large unless British Prime Minister Boris Johnson's government swiftly offers concrete proposals.

"The risk of a no deal remains very real. That will maybe be the choice of the United Kingdom but never the choice of the European Union," European Commission chief Jean-Claude Juncker told the European Parliament in Strasbourg.

If that happens, "the consequences are much more serious, much more numerous than you want to say," added EU chief Brexit negotiator Michel Barnier in remarks directed at pro-Brexit MEPs. 

"After Brexit, you will be accountable to the citizens," he told them.

The warnings came two days after Juncker and British Prime Minister Boris Johnson met in Luxembourg for talks and just six weeks before Britain is set to exit the bloc.

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

Juncker emphasised Britain still has not offered any viable solutions to rewrite a withdrawal agreement struck by Johnson's predecessor but rejected three times by the British parliament.

"I am not sure" a new deal will be reached, Juncker said.

"We have very little time left. But I am sure we must try," said the Commission chief, whose mandate ends on October 31 - the deadline for Britain to leave the EU.

Blame game

The strident messages came as Brussels and London blamed each other for moving towards a chaotic no-deal Brexit.

Barnier said "it is certainly not a question of pretending to negotiate," adding: "It is our responsibility to pursue this process with determination, with sincerity."

His words were taken as a dig at Johnson, who is seen by many in Brussels and London as running down the clock so that Britain leaves the EU at the end of next month with or without a new deal.

If so, Johnson risks falling foul of a law hastily passed by the UK parliament requiring him to ask for another Brexit delay -- a third -- by October 19 if no new deal is worked out with the EU.

Britain's parliament is currently suspended at Johnson's initiative in a move being challenged in the Supreme Court in London.

Adding pressure, the European Parliament on Wednesday voted a resolution noting the UK parliament's law on asking for another Brexit delay, but stressing there must be "reasons and a purpose for such an extension".

The decision on whether to grant an extension, however, is really up to the leaders of the other 27 EU member countries. They are to hold a Brussels summit on October 17-18, seen as the last chance to strike a deal.

"I continue to see the chance for an orderly exit," German Chancellor Angela Merkel told reporters in Berlin when pressed on the chaotic scenes out of Luxembourg.

"I didn't expect the visit to already provide a solution, it is very good that (Johnson and Juncker) spoke to each other," she said.

Bogged down in the backstop

London declared after Luxembourg that discussions with the EU on rewriting the withdrawal agreement would "soon take place on a daily basis," up from twice-a-week currently. 

But an EU spokeswoman said Wednesday that while Brussels was ready to meet "24/7", daily talks were not yet happening.

The thorniest issue between Britain and the EU is the "backstop" - an effort to guarantee that no hard border will spring up between EU member Ireland and the UK's province of Northern Ireland, while ensuring that the EU's single market remains protected.

Under the withdrawal deal reached last year, but rejected by the British parliament, the UK was to stay in the EU's customs union temporarily, in case talks towards a trade deal failed. 

But Johnson rejects that guarantee and is reportedly exploring ways that Northern Ireland alone could abide by EU agriculture and food standards without a full-fledged backstop.

"The new British government... has underlined the backstop aspects it doesn't like. That is not enough to reach a solution," Barnier said in Strasbourg. 

"We need to find a legally operational solution in the withdrawal agreement that fully answers each of the problems, addresses each of the risks," he said.

Juncker said "I hold no emotional attachment to the backstop" while remaining "profoundly attached to the goals it serves".