There are, as we will see, more than a few reasons to liken Sinn Féin to the United Kingdom Independence Party, but, by far the most amusing, involves the phlegm-soaked fury such parallels will trigger in both organisations. Indeed, Nigel Farage, cigaretting, beer-swilling leader of Ukip, has gone so far as to describe Gerry Adams as his “least favourite politician”. Why so mean, Nigel? You have so much in common. Neither of you was ever in the IRA. Neither has a racist bone in his body. Both of you are fervent nationalists with a taste for tweed and country walks.

To be less facetious, the two men find themselves leading parties in the most enviable of positions. If it really is better to travel hopefully than arrive then Sinn Féin and Ukip should do everything possible to enjoy their current journeys. Mr Adams’s party has been running bits of Northern Ireland officially for more than a decade (and unofficially for a good deal longer than that), but, in its modern incarnation, it has yet to wield any significant power in the Republic. Close to a century younger than Sinn Féin, the Farage Falange can’t even boast that level of engagement with the levers of authority.

Yet, if opinion polls are to be credited, the two parties are poised to become kingmakers at upcoming general elections. Others have been here before. Clann na Poblachta had their moment in the late 1940s. In Britain, the Social Democratic Party briefly shook the foundations during the early 1980s. What glorious fun it is be the face of Mainstream Insurgency (let’s capitalise that). One can leap on any populist bandwagon without having to worry much about who gets mowed down in its progress. After all, the Mainstream Insurgents aren’t running the country.

It was, of course, a Sinn Féin councillor who proposed the successful motion against the fluoridisation of water in Dublin City Council. You will not be surprised to hear that, in the 2010 election, a Ukip policy statement announced the party would “legislate to ban the use of fluoride in water supplies”. Easy to say when your minister does not have to answer questions on dental health.

A majority of readers will agree with Sinn Féin’s opposition to domestic water charges, but, unburdened by the responsibility of office, the party need produce only the sketchiest of figures to balance the books.

Ukip and Sinn Féin both trade on the same not-so-unique selling proposition: they are neither the government nor the official opposition. Everybody is always sick of politicians, but they’re a little sicker than usual at the moment.

It is at times such as this that Mainstream Insurgents – parties composed of politicians who pretend not to be politicians – find themselves very much in demand. Everybody wants to see them on the telly. No bottom has been tainted by contact with a ministerial limousine. Eccentricity is encouraged: Ukip and Sinn Féin have both been through the wars this week.

Mr Farage’s farcical problems will only add to the sense of antic carnival that follows Ukip about: Mike Read released a calypso in support of the party that, following complaints about his mildly offensive faux-Caribbean delivery, eventually drew an apology from the former BBC DJ.

Mr Adams’s continuing troubles concerning Maíria Cahill, the Belfast woman who accuses Sinn Féin of covering up her alleged rape, will not be nearly so easily dismissed. Yet we have repeatedly seen Sinn Féin erect stout firewalls between its current cuddly incarnation and the version that may once have had something or other to do with the IRA (or not).

The psephological runes send us in different directions. Sinn Féin has, surely, the greater chance of holding the balance of power. They have already won seats in general elections and the PR system is far fairer to third-placed parties than is the UK’s first-past-the-post system. Yet it is Ukip who have been over-performing at recent byelections – winning, as expected, in elderly Clacton and getting astonishingly close to beating Labour in Heywood and Middleton – whereas, against the odds, Sinn Féin somehow failed to take Dublin South-West.

Oh well. Maybe it would be better for both parties to fall just short of achieving kingmaker status. Nothing taints the Mainstream Insurgency more than a whiff of power. Whither Clann na Poblachta? The poor old Liberal Democrats are facing annihilation next May. The moment such parties get into office they are faced with the same uncomfortable compromises that made the larger parties seem so impure.

Mind you, as things stand, no larger party will countenance working with either Ukip or Sinn Féin. Hey, there’s something else they have in common. I do hope this comparison is annoying them both.