The Government will use the common travel area to try to exempt Irish citizens working in Britain from its proposed reduction in welfare payments to EU migrants during Brexit talks in Brussels.

The common travel area between the UK and the State, which predates both countries’ entries into the Common Market, is recognised in Protocol 20 of the EU Treaty.

The treaty states: “The UK and Ireland may continue to make arrangements between themselves relating to the movement of persons between their territories.

“Nothing in Articles 26 and 77 of the Treaty on the Functioning of the European Union, in any other provision of that Treaty or of the Treaty on European Union or in any measure adopted under them, shall affect any such arrangements.”

The Government will argue that the common travel area is an expression of the web of arrangements between the UK and the State on everything from social welfare to voting, which reflect the unique relationship between the two countries.

In response to a question in the House of Commons from SDLP MP Mark Durkan earlier this month, David Cameron suggested that he was open to exempting Irish citizens from any new social welfare arrangements for other EU citizens.

“I seem to recall from conversations I had with the Taoiseach that there are particular arrangements for the common travel area,” Mr Cameron said.

Common travel area

Although the common travel area has been in existence since 1923 and is recognised in the EU Treaty, it is based on administrative agreements between Britain and Ireland rather than legislation.

However, as a result of the common travel area, Irish nationals have a special status under British nationality law and British nationals have a special status under Irish immigration law.

Section 2 of the 1949 Ireland Act, enacted after the South became a Republic, states that “the Republic of Ireland is not a foreign country for the purposes of any law in force in any part of the United Kingdom”.

Social welfare arrangements between the two countries have been governed by a succession of bilateral agreements since the early 1960s.