In a call which made no reference to Conservative leader, and favourite to become Prime Minister, David Cameron's statement to the Ulster Unionist Party conference last year that he will "never be neutral on the Union", Mr Adams appealed for London to press for a united Ireland.

However, Mr Adams also pressed the Irish Government to be a persuader for a united Ireland.

Addressing a meeting of the British Irish Parliamentary Assembly in Swansea, which brings together British and Irish parliamentarians, Mr Adams said that there is a "particular responsibility for all parties in the Oireachtas (Irish Parliament) and particularly for the government in Dublin to actively work for reunification".

But he went on: "There is not only a democratic requirement on the part of the peoples of Britain to adopt a positive stance on how the Irish question should be finally settled, there is a moral imperative.

"It is one thing saying that unionists should not be frogmarched into a united Ireland; it is another to adopt the position of silence in the face of whether or not a united Ireland should come into being, in whatever negotiated form that will entail.

"The peoples of Britain have a duty to themselves, to unionists in particular, to the Irish in general, and even to the world, to stand up and speak their opinion on the issue of the reunification of Ireland.

"We have to persuade the British government to change its policy from one of upholding the union to one of becoming a persuader for Irish unity."

Much of the substance of Mr Adams' speech on Irish reunification, which made no mention of the one-time target of 2016 for a united Ireland, was an attempt to be conciliatory to unionists.

The West Belfast MP repeatedly stressed that the "political realities" of the Good Friday Agreement meant the constitutional future of the Province was settled until a majority of people in Northern Ireland vote for a united Ireland.

In words which would have been remarkable during the years when Mr Adams condoned the IRA's attempts to override the views of the majority and violently end British involvement, he said that it was for the people of the island of Ireland – both north and south of the border – to decide their constitutional future.

Mr Adams said that unionists had to be persuaded of the economic, cultural and constitutional merits of removing the border.

The Sinn Fein president also repeated his claim that Orange Order marches would "have their place, in a new Ireland albeit on the basis of respect and co-operation".

The Orange Order declined to comment on Mr Adams' remark.

Mr Adams also claimed that everyone's rights would be respected in a united Ireland, something which drew an angry response from TUV vice chairman Keith Harbinson: "Those who lost loved ones at the hands of the Provisional's terror machine will have little time for his claim that republicans don't seek to deny anyone their rights.