A no-deal Brexit is an “ugly prospect” that will oblige Ireland to impose customs checks on trade with Northern Ireland, the Irish government has warned.

Simon Coveney, Ireland’s deputy prime minister and foreign minister, made a grim prognosis on Tuesday of the “dire” consequences if the UK crashes out of the EU.

“A no-deal Brexit is an ugly prospect. It will put many businesses and many people under a great deal of strain,” he told a press conference in Dublin.

The tánaiste was speaking after the Irish government released a 117-page report outlining the country’s contingency plans for no deal.

“It will put political relationships on this island under a great deal of strain, in my view. It will make it more difficult for the institutions of the Good Friday agreement to function and it will be a fundamental disruptor to the all-island economy.”

Coveney said that to protect the EU’s single market, Ireland would check trade between the republic and Northern Ireland. “We will need to take some action somewhere … but we will not put checks on the border, or close to it.”

He said Dublin was working with the European commission to balance such checks with the need to avoid a hard border and protect the Good Friday agreement, but refused to say how this would be achieved. “There is no evil plan on a shelf somewhere.”

After a special cabinet meeting, the Irish government released the report outlining “very damaging” consequences of a no-deal Brexit for the political process in Northern Ireland, adding that it “risks significantly undermining wider community relations and political stability … with potential related security concerns”.

The report also reveals that additional gardaí have been deployed to border areas in recent months, and that more will be sent immediately in the event of no deal.

But “there should be no illusion” over the impact of Brexit on the island, with 11 risks identified including the undermining of community relations and political stability in Northern Ireland.

The report also put paid to Boris Johnson and Jeremy Hunt’s hopes that the EU will accept technology-based “alternative arrangements” for the Irish border.

It says it has been working with the European commission on this issue this year but “no one has yet come up with any alternatives that meet the same objectives as the withdrawal agreement”.

Report says since last year Irl has been working with EC on no deal.

"No one has yet come up with any alternatives that meet the same objectives as the Withdrawal Agreement." pic.twitter.com/YE5OTLksTO — lisa o'carroll (@lisaocarroll) July 9, 2019

The report says the government’s assessment is that there is now “a significant risk of a no-deal on 31 October” and preparation for such an event is a priority.

It warns of a potential £6bn cost to the Irish economy and an estimated increase in unemployment of 50,000-55,000.

“Preventing the emergence of a hard border on the island of Ireland remains of the highest priority,” says the report, but despite preparations “without the withdrawal agreement and the backstop, there are no easy answers”.

The biggest challenge will be how to continue cross-border trade involving animals and agricultural products.

In a no-deal scenario, all food and animals from Northern Ireland will be treated as sourced from a third country and not eligible to enter the EU without checks on traceability and disease.

As expected, the report does not say how these would be accommodated and says further talks with the European commission are needed.

The report warns of “disruption in north-south trade and the all-island economy due to tariffs and the imposition of various regulatory requirements”, and to cooperation in areas such as energy, road and rail connectivity.

The Irish government has been caught in a bind, refusing to discuss plans for the border in the event of no deal because that would risk legitimising a disorderly exit. At the same time, it is aware of its EU obligations to protect the single market from third-country goods.

The report says at least 24 hours’ notice will have to be given for goods going from the UK into Ireland. About 400 additional customs staff have been recruited with 190 staff in the Department of Agriculture to conduct import controls.

Séamus Nevin, the chief economist of Make UK, the British manufacturers’ association, said the plan to oblige UK traders to give 24 hours’ notice to Irish authorities was a “serious challenge to the viability of any Northern Irish manufacturer or farming business”.

Given the nature of modern supply chains and just-in-time deliveries, “the Dublin government is playing serious hardball and calling Her Majesty’s government’s bluff”.