- Video report by by ITV News Correspondent Martin Geissler
The Government is "confident" it can enforce new immigration controls on EU citizens without a hard border between Northern Ireland and the Republic of Ireland.
Avoiding checkpoints is the top priority for negotiating post-Brexit arrangements for its only land frontier with the EU, an official paper outlining the Government's position said.
The document says the UK wants preserve the Common Travel Area (CTA) between Northern Ireland and the Republic of Ireland after Brexit - allowing people to enter Britain free from routine border controls.
This is despite Ireland remaining part of the EU and accepting the free movement of citizens from the bloc.
It also suggested there will be no customs implications at all on the Irish border.
Critics say the proposals could offer a "back door" into the UK for people from the European Union after Brexit.
The UK proposals must now be debated with Brussels. But they have received a relatively warm welcome both in Ireland and in the EU.
Leaders in Dublin said avoiding a return to the paramilitary violence and terrorism of the past is crucial.
"The emphasis on the priority areas identified by the Government, including the Common Travel Area, the Good Friday Agreement, north/south cooperation and avoiding a hard border, is welcome," an Irish Government spokesman said.
"Protecting the peace process is crucial and it must not become a bargaining chip in the negotiations."
The Prime Minister personally reassured Northern Irish citizens that its "special ties" to both the UK would not be lost.
She said that Great Britain would not turn its back on its "unique and special relationship" with Ireland in a piece published by the Belfast-based Irish News paper.
She added that rights enshrined under the Good Friday peace accord, such as the right to claim Irish citizenship, would be protected after the exit from the European Union.
Ahead of the publication of the Whitehall document, the Irish Government said the peace process could not become a "bargaining chip" in Brexit talks.
But critics said the plans left more questions than answers.
Sinn Fein's Stormont leader, Michelle O'Neill, said the proposals were "big on aspiration but light on clarity".
"Whilst the British Government might say they don't want to see any kind of hard border or technology put in place, it will not be within their gift to deliver that," she said. "It will be the other European member states, who clearly think and believe we need to see customs controls."
Labour leader Jeremy Corbyn also "no one wants a hard border" but "at this stage of negotiations we can't rule anything in or out".
"I hope there can now be negotiations to make sure there is a continuation of free movement between Northern Ireland and the Republic," he added.
The Government is due to unveil further details about its immigration policy in the autumn.
The position paper says the UK believes an agreement on maintaining the Common Travel Area can be agreed in the first phase of its negotiations with the EU.
Other parts of the document raise issues about what impact customs arrangements on the Irish border could have on Britain's ability to strike new trade deals.
One passage talks about future "regulatory equivalence on agri-food measures", where the UK and EU agree to the same standards albeit with some flexibility.
Britain's animal welfare standards have been a major talking point, as after Brexit it does not have to comply with EU rules.
This has been highlighted over chlorine-washed chicken, which is banned by the EU but not in the US - and could form part of a future trade deal.