It is often said in favour of the Westminster electoral system that it tends to provide the voter with straightforward choices. The opening days of the campaign in Northern Ireland have provided a clear example of this, although arguably not in a good way.

The Conservative decision to stand down their original candidate in Fermanagh & South Tyrone underlines the potential flaws of first past the post elections, and greatly strengthens the case for electoral reform.

The decision means that the Conservatives will no longer be running in every constituency in the UK as David Cameron had originally pledged. In Fermanagh & South Tyrone they are instead backing a compromise unionist candidate who also enjoys the support of the DUP.

The result is likely to be an increasingly polarised contest in which the Sinn Féin incumbent, agriculture minister Michelle Gildernew, will try to squeeze the vote of the SDLP in order to hold the seat, having failed to secure a similar pact on the nationalist side.

The DUP and the Orange Order are pressing for another unionist unity deal in South Belfast to unseat the SDLP's Alasdair McDonnell. The local Conservative candidate has said she is willing to consider it.

It all adds up to a remarkable turnaround from the original aspirations of the UCUNF (Ulster Conservatives and Unionists - New Force) alliance between the Conservatives and the Ulster Unionist Party.

As recently as January, the Conservatives were aiming to break the mould of sectarian politics, talking up their willingness to to run Catholic candidates in some constituencies even at the risk of losing votes.

However, that same month saw the resignation of UCUNF's high profile Catholic recruits after the revelation of secret talks with the DUP at Hatfield House, the home of the Marquess of Salisbury.

Shadow Northern Ireland spokesman Owen Paterson denied there was any deal at the time, saying:

There is no question of us being involved any kind of electoral arrangement in Northern Ireland that involves other parties.

We are completely committed to standing together, as Conservatives and Unionists, to offer the people of Northern Ireland the opportunity to support national, mainstream and non-sectarian politics.

By last week, Paterson's position had changed significantly:

We recognise that Fermanagh and South Tyrone has characteristics that are unique within the UK.  It has been without any democratic representation for the past nine years.  It is the one constituency where there is currently an abstentionist MP, where a single cross community candidate could lead to the restoration of democractic representation at Westminster.  In recent weeks and months there has been an upsurge of public opinion across Fermanagh and South Tyrone to find such a candidate.

This is arguably disingenuous in a number of ways. For one thing, Paterson seems to have forgotten about the neighbouring seat of West Tyrone, where local hospital campaigner Kieran Deeny came second to the abstentionist Sinn Féin MP Pat Doherty in 2005, drawing votes away from both the SDLP and the UUP in the process. Given the circumstances of his nomination, the basis for presenting Rodney Connor as a 'single cross community candidate' looks thin by comparison.

Connor's candidacy would not have happened without the support of the DUP, which has made it quite clear that its objective is unionist unity against all nationalists, whether abstentionist or not. That is why it is proposing a similar pact in South Belfast, even though the current SDLP MP takes his seat at Westminster.

If they withdraw in South Belfast, the voices accusing the Tories of indulging in sectarian politics will only grow louder. As things stand, the u-turn on David Cameron's pledge to stand in every constituency raises a question that will resonate in Britain.

Owen Paterson has justified the decision on the basis that Michelle Gildernew's refusal to attend Westminster is undemocratic. Yet Gildernew stood on a clear abstentionist platform, and won a clear plurality of the vote. While many of those who voted for other candidates would have been opposed to abstentionism, its not clear that all of them would.

Gildernew has as much of a mandate on abstentionism as any MP has on any issue in a first past the post electoral system. It may be that abstentionism is a more fundamental issue than most, but if the system cannot produce a legitimate outcome on fundamental issues, surely that is a flaw in itself?

Ironically, the whole clamour for unionist unity would be unnecessary under the alternative vote, the very system which the Tories blocked in the wash-up at Westminster last week. By agreeing a pact, the Tories have underlined the bankruptcy of their case against electoral reform.