Theresa May is to offer free movement to Irish citizens in and out of Britain after the UK leaves the EU.
News of the offer of a "Schengen area" between Britain and Ireland came as the UK government prepares to publish a formal proposal to the EU on the future of the Northern Irish border.
By making this offer, the prime minister hopes that Taoiseach Leo Varadkar will become a key ally for Britain during the tough withdrawal negotiations.
Mr Varadkar has expressed his frustration at the failure of the UK government to ensure there is no return to the "hard" border between the North and the Republic.
Britain will also offer to track goods across the Irish border with CCTV cameras and automated number plate technology as part of a light-touch customs regime.
It comes alongside other documents setting out how Britain's involvement in the customs union will be after Brexit. More papers on fisheries and agriculture will be published next week. Other papers about the continued availability of goods for the EU and the UK, and confidentiality and access to official documents after Brexit will also be published.
The publications come as David Davis, the Brexit secretary, prepares a third round of talks with Michel Barnier, the EU's chief negotiator.
Mr Barnier is reported to have said the first two rounds failed to produce clarity on the Irish border, rights of EU citizens in the UK, and Britain's "divorce bill". His gloomy assessment cast doubt on whether enough progress will have been made to begin discussions in the autumn on a free-trade deal.
One source at Britain's Department for Exiting the EU said: "We've been crystal clear that issues around our withdrawal and our future partnership are inextricably linked, and the negotiations so far have reinforced that view. These papers show we are ready to broaden the negotiations."
The Ireland/Northern Ireland paper, which will be published this week, is the UK government's pitch to "protect the common travel areas and the Good Friday agreement", said a source.
"Ireland and the UK will be effectively its own Schengen area. The movement of people should not alter at all - you can come into Ireland as you do now. And any Irish person at the moment can work freely in the UK as can a UK citizen in Ireland."
Government sources in Dublin said they look forward to seeing detailed proposals from the UK government