The prospect of a united Ireland must remain an option in the wake of Brexit, Taoiseach Enda Kenny has said.
In an address to the British Irish Association in Oxford University, Mr Kenny said there was no evidence to suggest a border poll would bring about a 32-county republic if held now.
But he said Ireland should be treated the same as Germany after the fall of the Berlin Wall if people vote for reunification.
"The possibility of unity by consent must be maintained as a valid democratic option into the future," Mr Kenny said.
"That means that, if there were democratic consent to Irish unity at some time in the future, there must be a mechanism to ensure that a democratic decision can be implemented within the European Union, as was the case in Germany."
The Taoiseach said the Irish Government would shortly publish plans for organisations and individuals across the island of Ireland to have their say on the implications of Brexit.
He said that the upcoming Budget would not be significantly affected by the UK leaving Europe but it would take account of likely impacts.
"There is a long and difficult road ahead," he said.
"But I am confident that we can continue to manage relationships across these islands in a positive and constructive way, in the interests of all our people.
"It is a once-in-a-generation political and diplomatic challenge. Our greatest efforts must and will be dedicated to making this work."
Mr Kenny urged Britain not to look at the Brexit negotiations through a purely economic lens and warned that European leaders see matters of historic and fundamental importance at stake.
The Taoiseach also warned about the threat to the Northern Ireland peace process.
"At this time of profound change, there can be no room for old divisions to cloud the vision of the future. We must work together on all fronts to preserve and build upon what we have achieved. We must be thoughtful, pragmatic and generous," he said.
"We must look forward, and set a new horizon.
"Above all else, we must do nothing to undermine the foundation of the peace - the Good Friday Agreement, and subsequent agreements, that have transformed life on these islands."
Mr Kenny told the university audience that Ireland would seek to take opportunities from Brexit but said that the best outcome would be a close relationship between Britain and Europe.