Brexit will threaten peace in Northern Ireland, disrupt cross-border cooperation and create potentially lethal divides between British and Irish people in Northern Ireland, an 18-month study by academics has found.

In the most comprehensive study of the impact leaving the EU will have on the region, researchers also found that Brexit was seen as “manna from heaven” for Sinn Féin as it “mainstreamed” the topic of unification.

The Queen’s University in Belfast and Ulster University, in conjunction with the Committee on the Administration of Justice, conducted in-depth interviews, town hall meetings and consultations with authorities, producing six interlinked reports.

“This is a profound constitutional moment for Northern Ireland and the island of Ireland,” said Colin Harvey, professor of human rights law at Queen’s. “Brexit will threaten the peace process and weaken protections for human rights and equality. Many of these matters have simply been neglected in the discussions thus far and must change.”

The academics in the BrexitLawNI umbrella group found widespread concern about the long-term impact of Brexit on the relationship between the people of the entire island of Ireland. It ranged from anxiety that the change in status for the region would introduce a new focus on conflict between divided communities and on their differences.

The study concluded that the December joint report on Brexit signed by Theresa May and the European commission president, Jean-Claude Juncker, needed to be followed through with detailed protocols to ensure bespoke solutions reflecting the unique circumstances in Northern Ireland.

It said: “Common membership of the EU has been a basic building block of improved relations across these islands and on the island of Ireland in particular. Brexit has, therefore, promoted deep anxiety about future cooperation.”

Katy Hayward, a commentator on Brexit in Northern Ireland and reader in sociology at Queen’s, argued that generations of “severe social, political and economic challenges” in the central border region, not to mention the violence, had given way to cross-border cooperation.

She said the connections carefully constructed between once-rival communities remained vulnerable and that Brexit risked breaking those relationships.

She and her colleague David Phinnemore pointed out that Brexit could impose limits on this cooperation in border communities in counties in the central region, Fermanagh, Tyrone and Armagh, and their neighbours in the republic, Donegal, Leitrim, Cavan and Monaghan.

One local assembly member, the Alliance party’s Stephen Farry, was among those who highlighted the role of the EU in north-south relations in facilitating an open border. “Today is completely unfettered for people to engage in business and other aspects of life on a north-south basis,” he said.

The EU has also funded businesses in areas riven by violence, which conventional banks and financiers would have considered too risky.

The study also raised concerns over the future of all-island healthcare services. “With a population of 1.8 million, it would not be possible to provide certain specialised medical services in the region,” it noted.

Cancer services in the recently opened radiotherapy unit at Altnagelvin Area hospital in Derry, for example, are available to patients across the north-west of the island, regardless of which side of the border they live.

The all-island paediatric cardiology service based at a children’s hospital in Dublin allows children in Northern Ireland to receive life-changing heart surgery without having to travel to England to receive treatment.

BrexitLawNI concludes there is a clear need to lay down new protocols to preserve coexistence of communities and joint services to mitigate against the risks of the split on the island.

It recommends that the assumption that British and Irish citizens will continue to have the right to move freely between the two islands under the common travel area body of agreements and protocols is laid down in new legal codes. It notes there is no visible movement on this front in the UK or Ireland.

The Home Office hostile environment policy should not be rolled out in Ireland and official initiatives should be launched to tackle racial profiling, intimidation and violence, it says.