CS Lewis, the Belfast-born writer whose conversion from atheism to unwavering Christianity is as remarkable as his Chronicles of Narnia, pinpointed a moment on a train journey when he felt “holiness” come upon him. Having registered his newfound state of mind, there was no going back.

Sinn Fein is radiating the same ardour these days. Having resolved at its ard fheis in November that it is now willing to enter a future coalition government in Dublin, the erstwhile Dail abstentionists are exuding the zeal of the convert. Mary Lou McDonald declared in her inaugural speech as party leader last weekend: “Our purpose is to win: to win elections, to increase our political strength, to realise our ambition of being in government, north and south.”

If