Mr Adams said he believes a border poll will be held in the future, and called on the Dublin government to open up a consultation on unification.

“The debate about the future, about a new Ireland and the demand for a referendum on unity is growing,” he said. “Demographic and political changes in northern society are also playing an important role in encouraging this debate”.

Mr Adams pointed to recent elections in which the overall share of the vote for the main unionist parties fell significantly, falling by a fifth in the European elections. While the overall nationalist vote also fell slightly, it is still believed that nationalists will form the dominant community in future years.

The elections also showed increased support for Alliance, a ‘non-sectarian’ unionist party who ‘want Northern Ireland to work’, despite the sectarian nature of the statelet. The results show that Alliance has strengthened its claim to hold the balance of power within the Six County area.

Mr Adams said a plan now needs to be made to win the support of unionists for reunification in a Six County vote.

“This needs [to be] planned now. Not after the referendum. That is the one big lesson of Brexit. A referendum without a plan is stupid. So a referendum on unity must be set in a thoughtful inclusive process which sets out a programme of sustainable options, including phases of transition,” he wrote.

“What accommodations are needed to persuade political unionism that a united Ireland can work for it?”

He said the key to this to this is the need for “an agreed shared Ireland”.

“What happens to the political institutions established by the Good Friday agreement?” he asked.

“Winning support for a united Ireland is not just about persuading unionists although that is crucial. Everyone needs to be convinced of the advantages of unity – personal, economic, wages, health provision, environmental, cultural, peace, prosperity.”

He said there was a “constitutional imperative” to achieve a united Ireland. “There will be a referendum on Irish unity. I am confident of this. Winning that referendum is the biggest single challenge facing united Irelanders.”