The annual St Patrick's Day exodus to the United States is not what it used to be.

During the 1990s, Northern Ireland would gratefully empty its entire cohort of politicians, clutching suitcases full of green clover and emerald ties, unto a fleet of Boeing 747s bound for Washington.

Stormont's most ardent pedlar of Irish kitsch then is still, all these years later, its greatest enthusiast for a transatlantic jolly. Gerry Adams arrived in Boston on Saturday, scheduled for a full week of paddywhackery, focussed on promoting the goal of ‘Irish unity' among the island's diaspora.

He really needn't bother. The Sinn Fein president is already treated like a superstar by the section of Irish America he prefers to court.

Adams’s breakfast date on Sunday morning saw him lead a cross-party choir of senators and other New England legislators, who belted out rebel favourites, including the Boys of the Old Brigade.

Meanwhile, back in Northern Ireland, this newspaper added the final touches to a poll which revealed that 85% of Protestants and 26% of Catholics would vote to remain part of the United Kingdom in any border referendum.

Sinn Fein apparently accepts all the provisions of the Belfast Agreement which, when it is convenient, it invokes as if they were holy writ. That includes the vital sections, not frequently cited by republicans, which ensure that the people of Northern Ireland will determine their own constitutional future.

You might expect that Gerry would therefore have work to do closer to home, persuading unionists of the merits of ‘Irish unity'.

Instead, he has fronted something of a ‘world tour' to discuss the prospects of a 32-county republic with anyone other than voters who will actually decide whether or not it happens.

The London date took place last month and attracted the usual suspects; ‘Red’ Ken Livingston joining Ronan Bennett, novelist and sometime Guardian contributor, at a venue provided by the TUC.

It was, no doubt, a cosy gathering, but whether the target audience comprises a set of former Trots from London, or the cream of the Irish American establishment in Massachusetts, the common denominator is that these people should have little or no say in the constitutional future of Northern Ireland.

From recent pronouncements it is clear that Gerry Adams now accepts that there is something which sets Northern Ireland apart from the rest of the ‘Irish nation'. “We need to look at what they [unionists] mean by their sense of Britishness,’’ he conceded, during a speech in Cardiff.

The Sinn Fein president has suggested a range of concessions which might reconcile ‘them’ (unionists) to a united Ireland. These revolve mainly around Orange parades.

Adams is making a simple category error. He uses ‘unionist' or ‘British' as shorthand for ‘Ulster Protestant', ignoring the inconvenient fact, highlighted by the Belfast Telegraph's poll, that a quarter of Catholics also favour Northern Ireland's position within the UK.

The difficulty is that, in spite of his supposed best intentions, Adams hasn't listened to unionists during all his years in politics. After all, by a ‘sense of Britishness', nothing terribly mysterious is implied.

Simply, unionists have a clear, rational and defensible political allegiance to the United Kingdom, which Sinn Fein is not entitled to override, other than through persuasion and argument. Unionists are British because they want to remain part of the United Kingdom and enjoy representation at Westminster.

The roadblock to ‘Irish unity’ lies, not outside Ireland, not in the Machiavellian machinations of the London Government, but in the hearts and minds of 55% of people in Northern Ireland who wish to remain part of the UK.

So Gerry Adams might have fun courting acclaim from armchair republicans in Boston, having a good old sing-song and decking himself in green, but he won't advance the goal of ‘Irish unity’ one iota on his travels. That prize is within the gift of voters in Northern Ireland.

Owen Polley is a unionist blogger and commentator