* Ireland says time running out for a deal
* Brexit minister says moment of truth coming
* UK PM Johnson criticised for Brexit language
* Aide Cummings tells opponents to deliver Brexit (Recasts, adds Ireland's Coveney, Brexit minister)
BRUSSELS/LONDON, Sept 27 (Reuters) - Irish Foreign Minister Simon Coveney warned on Friday that time was running out for Britain and the European Union to hammer out a divorce deal with the British Brexit minister also saying the moment of truth was approaching.
Prime Minister Boris Johnson has vowed that Britain will leave the EU on Oct. 31 whether or not a deal has been agreed with the bloc, and while both sides say they are keen to reach an agreement, there is little sign of the deadlock being broken.
Johnson's opponents say leaving the EU without a deal to keep most of its trading arrangments in place would plunge Britain into economic chaos. The government says it has made preparations to avoid serious disruption.
The EU agreed a withdrawal package with former Prime Minister Theresa May but this was rejected three times by the British parliament over the "Irish backstop" - an insurance policy to prevent the return of a hard border between the British province of Northern Ireland and the Irish Republic.
After a meeting with EU Brexit negotiator Michel Barnier in Brussels, Ireland's Coveney said negotiations had to be on the basis of a "serious proposal" from the British on how they would replace the backstop.
"That hasn't happened yet and until there is a serious proposal in writing ... then the gaps that are wide at the moment will remain. And time is running out," he told reporters.
Barnier said the bloc was firmly united on insisting on a legally operative fix for the Irish border issue, saying it needed to avoid a hard border and protect the integrity of the EU's single market.
"The onus is on the British prime minister and his team," Coveney said, adding that Ireland was open to extending the Brexit departure date. "An extension is preferable to no deal," he said.
Britain is due to present concrete legal texts on their Brexit plans next week after the Conservative Party conference.
This month, British lawmakers forced through a law which compels Johnson to seek an extension to Brexit unless he has agreed a new deal with the EU by Oct. 19 or got parliament's approval to leave without an agreement, an outcome a majority of lawmakers and many businesses believe would be calamitous.
Johnson has repeatedly said he would abide by the law, which he has dubbed the "surrender act", but Britain would definitely leave on Oct. 31 without explaining the apparent contradiction.
"We will obey the law, but we're confident we can come out on Oct. 31 and the best way to do that is to get a deal," Johnson told reporters on Friday.
"That's why the surrender act is so damaging," he added. "It has had the effect with our European friends making them think: 'maybe parliament can block this thing, maybe they will be forced to extend.' If you're in a negotiation that obviously makes it more difficult."
Britain's Brexit minister Stephen Barclay also met Barnier on Friday and said there was a long way to go until they reached a deal.
"I think we are coming to the moment of truth in these negotiations," Barclay said in a television interview, repeating the message that the backstop had to go but a deal could be struck with good will on both sides.
With agreement still some way off, Britain's exit from the European Union still remains clouded in uncertainty three years after the vote to leave, and the country remains utterly divided with animosity reaching ever new levels.
Parliament reached boiling point on Wednesday when Johnson and his opponents spent hours hurling allegations of betrayal and deceit across the chamber of the House of Commons.
Opposition lawmakers accused Johnson of stoking hatred and cast him as a cheating dictator. One called him a liar. Johnson dismissed death threats against female law-makers as "humbug" and accused his opponents of "surrender" to European leaders.
On Thursday, Johnson's most senior adviser Dominic Cummings told politicians they should not be surprised by the mounting anger and the atmosphere would get worse unless Brexit was delivered.
"If you are a bunch of politicians and you say that we swear we are going to respect the result of a democratic vote and after you lose you say 'we don't want to respect that vote'. What do you expect will happen?" said Cummings, the mastermind behind the 2016 campaign to leave the EU.
Britain's leading bishops intervened on Friday to say all sides should moderate their language.
Johnson, the public face of the Vote Leave campaign, has also said that tempers need to calm down and that resolving Brexit would "lance the boil". The Conservative Party elected him as leader in July on his promise to break the impasse and take Britain out of the bloc by Oct. 31.
But he has faced defeat at every turn, losing his parliamentary majority, every vote in the legislature, and a groundbreaking case in the Supreme Court which overturned his decision to suspend the assembly.
Cummings rejected a suggestion that the government would back a "soft Brexit" - one that keeps Britain more closely aligned to EU rules - in order to get a deal by Johnson's October deadline.
Despite the uncertainty and turmoil, Cummings said they were not under any pressure and the situation was far less difficult than winning the 2016 referendum.
"This is a walk in the park compared to that. All the Vote Leave team, we are enjoying this, we are going to win, we are going to leave, don't worry," he said. (Writing by Kate Holton and Michael Holden; Editing by Angus MacSwan and Toby Chopra)