Agenda: Constitutional threat from across the water that makes Evel look like child's play

This fixation with constitutional matters in mainland Britain has allowed eyes to wander from Northern Ireland, which has so often been the centre of constitutional politics in Britain. It seems to many in the corridors of power that, after the Good Friday Agreement and the subsequent power sharing deal, that was it; job done.

All things concerning Ireland (Northern and the Republic) has received limited attention in the UK in recent years.

In particular, the astonishing rise of Sinn Fein in the Republic, which presents far more challenging issues than if an MP from Govan has a vote on transport issues in Gillingham, has been absent from the constitutional discourse.

For the first time in living memory, Sinn Fein have representatives covering each of Ireland's historic 32 counties in some form, from local councillors to MEPs.

Since ending their abstention to elections to the Republic's lower house of parliament (Dail Eireann) in 1986, the party entered electoral politics in the country. Fielding candiates in the subsequent 1987 election, they could only muster a measly 1.9 per cent of the popular vote.

Those days are long gone. At the last election in 2011, Sinn Fein came fourth with just under 10 per cent of the vote and with, long-time party leader Gerry Adams entering the Dail, he has became one of the leading figures of public life in the Republic.

Since that election, Sinn Fein have gained unprecedented levels of support. They have managed to carve their own niche in the country's politics. The governing Fine Gael-Labour Party coalition have introduced harsh austerity measures, with none so potent as the "water charges" legislation.

Three opinion polls last month placed Sinn Fein above 20 per cent, two of which have them as the single most popular party.

Alarms bells should be starting to sound in Downing Street.

Through their administration of austerity in the governing coalition, the Irish Labour Party, like the Liberal Democrats in Britain, have seen their core vote melt away in recent elections and opinion polling. Their vote seems to be transferring en masse to Sinn Fein, the self-proclaimed alternative to austerity in the Republic.

This upsurge in support for Sinn Fein, if it continues, means that they could find themselves either as the largest party at the next election (which must be held no later than April 2016) or, indeed, holding the balance of power with parties relying on their support to form a government.

Elections to the Dail use proportional representation and a string of independent candidates are regularly elected also. This creates an unpredictable nature to Irish politics, and at no other time have the historic leading parties of Fine Gael and Fianna Fail looked so weak. It all equates to fertile ground for further Sinn Fein electoral success in the country.

Gerry Adams as Taoiseach or his party within an Irish government, at any level, would represent an astonishing crisis for the UK. Imagine Mr Adams and Sinn Fein dictating the relationship between the two states. His party would be in effect part-governing the entire island, not only through the power sharing agreement in Northern Irish assembly but also through the North/South Ministerial Council which coordinates legislation on certain issues throughout the island.

How would the Unionist community in Northern Ireland react to Sinn Fein in power of the Republic? Let us not forget an issue surrounding the flying of a flag from a municipal building caused weeks of rioting and disorder in Belfast. It would not be presumptious to assume they'd deem it a threat to the long term constitutional position of Northern Ireland in the United Kingdom.

The rise of Sinn Fein in the Republic of Ireland presents a potential constitutional crisis that would make Evel look miniscule in comparison. Its time the Biritish Government started paying more attention to Irish constitutional affairs.