Almost 1,000 police officers from England and Scotland are to begin training for deployment in Northern Ireland in case of disorder from a no-deal Brexit, the Guardian has learned.

The plans were put in place after Police Service of Northern Ireland (PSNI) chiefs asked for reinforcements to deal with any trouble that arises from a hard border. The training for officers from English forces and Police Scotland is expected to begin this month.

The news came on a day of growing concern that a no-deal Brexit is becoming a distinct possibility, on which:

• The Irish prime minister, Leo Varadkar, said Ireland was “now preparing for no deal with the same level of seriousness that we would” Theresa May’s deal, adding that he and the German chancellor, Angela Merkel, had spoken and agreed that there could be no change in the offer to the UK.

• EU leaders rebuffed May’s hopes that her round of phone diplomacy could prompt any movement, saying “negotiations have concluded”.

• May’s attempts to woo the Democratic Unionist party were again rejected after two days of intense negotiations, making the chance of victory for the prime minister in the crucial mid-January vote on her deal still more remote.

The prospect of large numbers of English and Scottish officers being deployed on the streets of Northern Ireland after 29 March could anger republicans and complicate efforts to restore the power-sharing executive at Stormont, which collapsed in 2017.

The option of reinforcements is deemed necessary to cover the possibility of civil disorder arising from disquiet about border arrangements that could be put in place after a hard Brexit.

The police training will require officers to be pulled from their regular duties. It is needed because some of the equipment and tactics used in Northern Ireland vary from those used in the rest of the UK.

The PSNI is yet to make the formal request under mutual aid arrangements, which are in place to enable local police forces to help each other in times of heightened demands.

A team at the National Police Chiefs’ Council are planning for a no-deal Brexit which will also see extra demands on policing across the UK. Demands for reinforcements for Northern Ireland in the event of no deal come as forces with major ports in their jurisdiction prepare for chaos, especially at Dover in Kent.

Plans for a national mobilisation of police, which were devised after the 2011 riots across England, are being revised and adapted for the tensions thrown up by a no-deal Brexit.

The size of PSNI’s request for reinforcements from the rest of the UK because of Brexit is roughly double those it has made in recent years for the province’s marching season, when extra officers are needed to police tensions between Protestant and Catholic communities.

In remarks rejecting the government’s latest overtures to the DUP, the party’s Nigel Dodds said fears of a hard border were “nonsense propaganda”, adding: “With this clarity emerging in London, Dublin and Brussels, there is evidently no need for this aspect of the withdrawal agreement.”

Sources suggested that the meetings with May and the Conservative chief whip, Julian Smith, were “Groundhog Days” for those present. Significantly, there are no scheduled plans for further meetings between the prime minister and the DUP to discuss the backstop, the fallback plan to prevent the return of a hard border on the island of Ireland.

But Varadkar said the EU’s existing offer would not change. Saying he had “given up speculating” on whether the UK would leave the EU without a deal, he added that despite May’s attempts to find support in her phone calls to Merkel and others in recent days, European leaders stood united on the issue.

“We’re happy to offer reassurances and guarantees to the UK, but not reassurances and guarantees that contradict or change what was agreed back in November,” he said.

Irish and British government officials would be speaking by phone on Friday, Reuters reported Varadkar as saying. He added that the calls would be followed up with “direct contact” between the two prime ministers as needed.

Like its counterpart in the Republic of Ireland, the UK government is stepping up plans for a no-deal scenario. The Brexit secretary, Stephen Barclay, said the government was to “accelerate our no-deal planning further” to include a public information campaign, using radio and social media to raise awareness about the need to prepare.

With only 85 days until the Brexit deadline, the government has been pushing for further guarantees on the backstop.

But a European commission spokeswoman said talks could not be reopened. “The deal that is on the table is the best and only deal possible and the EU27 leaders confirmed on 13 December in their conclusions that it will not be renegotiated,” she said. “As I understand for now, no further meetings are foreseen between the commission’s negotiators and the UK’s negotiators, as negotiations have indeed concluded.”

An EU source said nothing had happened regarding Brexit over the last 10 days, although May had spoken with the president of the European council, Donald Tusk, on Wednesday. The prime minister spoke to Merkel twice during the holiday period.

The EU’s reluctance to reopen talks reflects the deeply held view among officials that the bloc has gone as far as it can in offering reassurance on the backstop.

“There is a general frustration with the whole process. We have worked very hard for the last 18 months,” said one EU source. “We have compromised, we have done a lot to get this nailed down on time.”

A National Police Chiefs’ Council spokesman said that forces “continue to prepare for possible eventualities as exit from the European Union draws nearer” but emphasised that no formal request had yet been made.

Mark Hamilton, assistant chief constable of PSNI, said that while there was not yet reason to trigger mutual aid, precautionary measures were sensible. “Our view is that it is better to have precautionary plans in place and not use them, than find we may need additional police support but cannot have it because we have not alerted the NPCC in advance.

“While we plan for mutual aid, we will only ever use it when it is absolutely necessary and proportionate.”

• This article was amended on 4 January 2019 because an earlier version implied that the mutual aid process had been triggered, but the PSNI has yet to make the formal request. Statements supplied to the Guardian after publication from the National Police Chiefs’ Council and PSNI were added. In addition, the picture used in an earlier version was removed as it did not accurately reflect the content of the article.