Irish citizens in Britain could lose their right to live, work and get NHS services in the country after Brexit, according to a new report that warns that the special status enjoyed by thousands of Irish in the UK is far from secure.

Laws governing their status are a “patchwork” that could fall apart under post-Brexit political and practical pressures, says the report, which comes before Monday’s launch of a campaign urging the UK government to pass legislation that would guarantee the longstanding rights of Irish citizens.

The document, drawn up by legal experts on behalf of the Traveller Movement (TM), concludes that many of the rights currently enjoyed by Irish nationals in the UK exist only because they are EU citizens. It warns that the Irish might be caught up in the so-called “hostile environment” policy on migrants that Theresa May originally created when home secretary, and which critics say is increasingly affecting a much wider range of people. The report highlights a range of scenarios that could arise if the UK ends the special rights of EU citizens without making new legal provision for the Irish. These include exclusion from free NHS treatment, cash benefits and certain social welfare payments.

The lack of clarity on the status of Irish nationals could also make the British citizenship of their children unclear, warns the document.

“The British government has consistently promised that Brexit will not weaken the situation of Irish citizens in the UK, or the movement of Irish citizens to and from the UK. Yet it has not made public how it will deliver on this promise,” said report author Simon Cox, a leading migration lawyer and barrister at Doughty Street Chambers. “A close look at current British laws shows a patchwork that may fall apart under post-Brexit political and practical pressures.”

Quick Guide What is the EU withdrawal bill? Show What is the EU withdrawal bill? The EU Withdrawal Bill – once known as the Great Repeal Bill – is going through the House of Commons to repeal the 1972 European Communities Act and transpose all existing EU legislation into domestic UK law, which will avoid a 'cliff-edge' change on the day after we leave the EU. Parts of the bill have been highly controversial, and MPs have tabled hundreds of amendments to try and change its wording, including a significant number of Conservative rebels. Some of the key controversies include its use of so-called Henry VIII powers, which will give government ministers the power to tweak the wording of laws to make sure they make sense in UK legislation - but those changes could take place without having to go through parliament. MPs have called this a "power grab" by the government. The government estimates around 800 to 1,000 measures called statutory instruments will be required to make sure the bill is applied correctly. Other concerns include the government's decision not to include the EU charter of fundamental rights in the law being transposed. Other amendments are attempts to affect the Brexit process, including legislating for a transitional period and giving MPs a binding meaningful vote on the deal secured by Theresa May, before the deal is finalised.

The TM commissioned the research following concerns about the impact of Brexit on Irish travellers in Britain, a distinct ethnic minority of about 100,000 people who already face significant prejudice.

A fear among those representing this group relates to an existing UK law that allows the deportation of Irish citizens who are not also British citizens. The report asserts that this calls into question the UK government’s rhetoric that Irish citizens and British citizens enjoy reciprocal rights, when in fact only the Irish government has renounced the power to deport Britons.

Yvonne McNamara, TM chief executive, said: “There are certain groups, such as Irish travellers, who are much more vulnerable than others if laws are unclear and left to the interpretation of employers, landlords and officials.”

The document is released against the background of increased concern about the language used by some sections of the media, as well as among Tory and Ukip politicians who have sought to blame Ireland for the current impasse in the Brexit talks.

Conor McGinn, a Labour MP, said: “I am very worried about this moment in British and Irish relations. Outside Northern Ireland no one has benefited more from the good relations than the Irish community in Britain, but now people are growing very concerned at some of the rhetoric coming from the Tory backbenches and the rightwing press, which does lend itself to hostility to the Irish community. Increasingly bellicose statements about Ireland do have an impact on that community.”

McGinn is leading an amendment to the EU withdrawal bill, which is making its way through parliament this week, which he believes would secure the rights of Irish citizens in Britain.

McGinn said of his amendment: “It would ensure that the rights, status and entitlements of Irish citizens would remain completely unchanged after we leave the EU. With all of the focus on the border this has not received the attention that it merits but a lot of Irish people, particularly older ones, are anxious about it. They have raised families and are concerned and confused when all that we really have to depend on are a series of platitudes from the government.”

The move comes as data analysed by the Institute for Public Policy Research (IPPR) reveals considerable regional variations in EU migration to the UK. There was a net annual increase of just 2,000 EU citizens to the south-west last year. The north-west and Wales attracted just 4,000 more EU citizens, the north-east just 3,000, while London attracted 22,000.

May told parliament in June that new post-Brexit arrangements for EU citizens would not apply to Irish citizens. She insisted that their rights would continue to be guaranteed under the common travel area, the “open borders” area comprising the UK, Ireland, the Isle of Man and the Channel Islands.

“We will preserve the freedoms that UK and Irish nationals currently enjoy in each other’s state. And Irish citizens will not need to apply for permanent residence to protect these entitlements,” she said.

The report has been sent to the Department for Exiting the European Union along with a letter from the crossbench peer Lord Alton, who says: “The paper enclosed clearly demonstrates that the rights of Irish citizens – future generations and those already living here – are currently at risk and need to be secured with urgency.”

He predicted that there would be heightened public expectations about post-Brexit measures directed at people who are not British citizens, adding: “Can we safely say that the British government has ensured that Irish citizens would be protected from such measures? I am afraid that we cannot.”