The EU’s top Brexit negotiator cast further doubt on the UK leaving the bloc with a deal as tension rises between the government and opposition before Parliament returns from recess next week.
Writing in The Sunday Telegraph, Michel Barnier said he was not optimistic that a no-deal scenario would be avoided, but he said both sides should continue to "work with determination".
British Prime Minister Boris Johnson has said that the UK will leave the bloc on October 31 without a deal if Brussels does not return to the negotiating table.
Mr Johnson has suspended Parliament to avoid MPs blocking a no-deal scenario.
The move was met with outcry in Westminster and across the country, as tens of thousands took to the streets at the weekend to protest against the proroguing of Parliament.
Mr Barnier said there was still confusion over the Irish backstop, which seeks to prevent the return of a hard border between Northern Ireland and the Republic of Ireland by provisionally keeping the UK in the Customs union with the EU.
He said the backstop was not about changing the constitutional status of Northern Ireland.
Mr Barnier said that was “none of the EU’s business” and was for British and Irish governments to decide.
“The EU is ready to explore all avenues that the UK government may present that are compatible with the withdrawal agreement," he wrote.
"Uncertainty has festered for far too long in the UK, in particular in Northern Ireland, as well as in Ireland and all other EU countries, for that matter."
Mr Johnson wants to abandon the backstop, which was introduced by former British leader Theresa May, but he has yet to come up with an alternative.
The EU has repeatedly said that Mrs May’s withdrawal agreement could not be amended.
Mr Barnier said that even in an event of no-deal, the UK’s financial and other obligations from its EU membership would not be wiped.
He said that in such an event, the EU would move to protect its own interests and there would be “no transitional period or mini-deals”.
“The EU cannot prevent the UK from choosing a 'no-deal’ scenario," Mr Barnier said.
"I would fail to understand the logic of that choice, though, as we would still need to solve the same problems after October 31,
“Many people in the UK understand that and I would be surprised if they succumb to the idea that the EU is to blame for a difficult political situation in the UK."
On Sunday night, the British government launched the country’s biggest public advertising campaign to prepare people for Brexit.
The taxpayer-funded Get Ready for Brexit campaign urges the public to visit a new website to prepare for a no-deal scenario.
After meeting Conservative whips over lunch on Sunday at his Chequers country retreat, Mr Johnson threatened to purge MPs who voted against the government on Tuesday.
Conservative rebels will not stand as candidates for the party in an election, Sky News reported, quoting a senior source at the Tory whips' office.
Earlier on Sunday, shadow Brexit secretary Sir Keir Starmer told the BBC that MPs would introduce a bill to Parliament seeking to block a no-deal exit from the EU.
But Cabinet minister Michael Gove refused to say whether the government would abide by legislation designed to stop the UK leaving the bloc without a deal.
"Let's see what the legislation says," Mr Gove said.