As commentators now make a habit of pointing out as the farce of the leaders’ debates drags on, the Democratic Unionist Party is the fourth-largest party in the House of Commons. From his office in Belfast Peter Robinson, who lost his own seat in 2010, commands a caucus of eight MPs.

Nor does this represent the upper limit of the party’s potential strength. Both Robinson’s old seat of East Belfast and North Down, currently held by Labour-leaning independent Lady Sylvia Hermon, could fall into the party’s hands in 2015, and there are one or two seats which could potentially return a unionist MP in the right circumstances.

Back in 2010 it was regularly pointed out that, as the only other centre-right party in the House of Commons, they could prop up a minority Conservative administration.

Yet despite this strength and potential relevance, the national broadcasters do not currently plan on including the DUP in the election debates – to which they have invited Plaid Cymru, who possess only three MPs. The DUP are not happy about this.

A former BBC producer provides an insight into the decision process:

“If you put the DUP in, you’ve then got the SDLP, Sinn Féin, the Alliance, the official unionists and that really is Northern Ireland politics which doesn’t translate to the whole of the UK,” he said.

“So, I hope there will be measures to make sure that viewers in Northern Ireland will get proper debates featuring Northern Ireland politicians in Northern Ireland, but I think once you start putting Northern Irish politicians into the UK debate it becomes completely unworkable.”

It is true to point out that Northern Irish politics doesn’t translate to the whole of the UK – but then neither the Scottish National Party nor Plaid Cymru are offering UK-wide programmes either.

Nor for that matter have the Greens been a UK-wide party since 1990, although their much vaunted membership totals add the Scottish and Northern Irish parties to the English and Welsh total.

If these parties are being included because they might potentially form part of a national governing coalition or deal, whether they themselves are national or not, then there are no grounds for excluding the DUP, Sinn Fein, SDLP or Alliance.

Yet if the DUP resent Northern Ireland being tucked away in its own little box in the minds of the political nation, they have done as much as anyone to put it there.

Where the old Official Unionists (now the Ulster Unionists) at least had an integrationist wing and a historical connexion with the Conservatives and mainland politics, the DUP are not the product of any pan-UK political tradition.

They instead evolved out of Ian Paisley’s radical Protestant Unionist Party during the Troubles, which although briefly integrationist in bent swiftly evolved into a stridently tribal operation.

A unionist from the mainland looking at Northern Ireland would find little familiar and much unpleasant in the DUP. Like the fauna of some isolated island, they are endemic to their local political environment.

Moreover, despite modern efforts they have never broken out of the strictly communitarian, confessional electoral box Paisley built around them, and have reached out neither to Northern Ireland’s Catholics nor to mainland politics.

Indeed, it has been remarked that if you swap “British rule” for “direct rule”, it can be hard to tell the DUP’s resentment of Westminster rule from Sinn Fein’s.

None of this detracts from the fact that their probable eight-to-ten MPs will be just as capable as Plaid’s handful of contributing to the next government of this country, and that they warrant inclusion on that basis. (Whether Sinn Fein do, in light of their refusal to take their seats, is another matter).

But if the proudly British unionists at DUP HQ are discomfited at how totally absent they are from the national conversation, perhaps this might prompt them to do something about it.