Common Travel Area between Ireland and the United Kingdom

From the link above

"On 8 May 2019, the Irish and UK governments signed a Memorandum of Understanding (pdf) reaffirming the Common Travel Area and identifying the rights and privileges of Irish and UK citizens within the CTA. It also reaffirms the commitment to maintain the CTA following Brexit"

and

"The UK’s withdrawal from the European Union (EU) will not affect the rights of Irish citizens and UK citizens within the Common Travel Area. The right to live, work and access public services in the Common Travel Area will be protected, regardless of the outcome of the Brexit negotiations."