A pro-Europe think tank has suggested that Northern Ireland could join a European free trade association after Brexit.

The approach would maintain Northern Ireland’s membership of the European Union's single market and address many of the concerns surrounding a hard border with the Republic, the European Policy Centre said.

The European Economic Area agreement unites the EU member states and Iceland, Liechtenstein and Norway into an internal market.

It allows free movement of goods, capital, services and people for work, the latter a contested provision ahead of Brexit talks.

The EPC said: "The European Economic Area option would, however, ensure a high degree of continuity with the status quo.

"With the EEA there would be clarity; the economic uncertainty surrounding Brexit would therefore be reduced."

Britain is seeking privileged access to the EU's single market at the same time as controlling EU immigration once the UK has left the EU.

The policy centre acknowledged joining the EEA would be no panacea for the challenges associated and would pose political and constitutional problems for the UK while requiring its founding agreement to be amended.

It said the measure would address a range of the concerns set out in the only substantive statement so far to emerge from the Northern Ireland Executive on Northern Ireland's interests in the case of Brexit: the August 2016 letter of the then first minister Arlene Foster and deputy first minister Martin McGuinness to Prime Minister Theresa May.

The letter stressed that Brexit could not be allowed to compromise cross-border efforts to tackle organised crime and those opposed to the peace process.

The ministers also said it was critical to the economy that businesses retained their competitiveness and did not incur additional costs.

It highlighted the need to retain access to sources of skilled and unskilled labour in the EU.

The vulnerability of an agri-food sector reliant on EU subsidies was also raised, as were concerns that a proportion of billions of euro of EU funds for projects in Northern Ireland may not be drawn down due to the exit.

The report from the EPC said under its proposal there would be no participation in the Common Agricultural Policy or the EU's structural funds; and Northern Ireland as part of the UK would be outside the customs union, which would allow the UK government to conclude its own trade agreements with other states.

Sinn Féin has supported a vocal campaign calling for special status for Northern Ireland post-Brexit.

Northern Ireland Secretary James Brokenshire has ruled the move out, and DUP MP Sammy Wilson, who represents the largest party in the country, has said all parts of the UK should leave the EU on an equal basis.

Southern EU leaders to discuss Brexit 

Meanwhile, leaders of southern EU nations will meet in Madrid today in a show of unity and to back greater European Union integration after Britain began the process of leaving the bloc.

Spanish Prime Minister Mariano Rajoy and the leaders of France, Italy, Portugal, Greece, Cyprus and Malta will gather at El Pardo palace outside Madrid.

The meeting will be a chance to "launch a message of unity and commitment to the project of European integration at a decisive moment in our history," the office of Spanish Prime Minister Mariano Rajoy said in a statement.

"Europe must continue to work to address the issues of greatest concern to its citizens and strengthen its project of integration," the statement continued.

Also on the summit agenda is the issue of immigration, of particular interest to southern EU states on the frontline of the problem.

The leaders will also discuss economic, social and defence policies.

The meeting of the leaders will be the third by the group following gatherings in Athens in September and Lisbon in January.

Southern European leaders have sought at past meetings to forge a common front on growing challenges, from the refugee crisis to Brexit, and to counter the influence of nations in northern Europe within the bloc.

The date of the Madrid meeting was announced on 29 March, the day that Britain formally began the two-year process of quitting the EU.

The Syria crisis will also be discussed in Madrid, a French diplomatic source said.