One of the great things about running any of the big city marathons is the sightseeing that can distract you from the crushing pain in your limbs. In the London Marathon, at mile 25, I passed my old office in parliament. In Berlin the route criss-crosses the site of the Berlin Wall. And in Dublin, I’ve run by the General Post Office (GPO), Ireland’s iconic building.

At midday on Easter Monday 1916, 150 men led by James Connolly marched along Sackville Street and into the GPO. Within hours, Pádraig Pearse, flanked by armed supporters, was standing on its steps and reading the proclamation of the Irish republic. History celebrates it as the birthplace of Irish nationhood.

In response, the British launched headlong assaults on rebel-occupied buildings. They deployed field guns from the nearby Trinity College and the anti-submarine patrol vessel HMY Helga bombarded the city centre from the River Liffey. Within a week the rebellion was defeated. In total, 485 people died that Easter week, most of them civilians. The British army and police lost almost twice as many men as the rebels.

However, it was events in the stone breakers’ yard of another of my marathon landmarks that transformed the rising and the post-rebellion demands for independence. Within days of military victory, Britain engineered a bloody and painful defeat that helped dislodge most of Ireland from its grasp. Kilmainham Gaol is an unremarkable site but it’s where Britain took revenge. After secret trials, each of the proclamation’s signatories and the volunteer commanders was blindfolded and executed. Only Éamon de Valera, the future Taoiseach, was spared on account of his American birth. It was described by W B Yeats in his famous poem as “a terrible beauty is born”; no other event in

Irish history, including the famine, has inspired so much debate, song and poetry.

The impact was electrifying. Dublin, which in that week had endured a strange mix of armed insurrection but widespread ambivalence, rallied behind its “martyrs”. Ireland was incensed. Irish recruitment for the British army’s Western Front stalled. Although most of the rebels weren’t “Shinners” or IRA, support for Sinn Fein surged.

The Irish question had dominated British politics since before the first home rule bill of 1886. It had helped tip the balance away from the Liberals in favour of the Conservatives and their new Liberal Unionist allies. In an early outing for their 2015 election playbook, the Tories claimed that Gladstone, Asquith and Lloyd George were all in the pocket of unreliable nationalist MPs – of the Irish (not Scottish) variety, of course.

The party differences were stark. Gladstone famously declared, “My mission is to pacify Ireland,” as he disestablished the Church of Ireland and reformed land rules in favour of Irish tenants. In contrast, many Conservatives shared the assessment by Lord Salisbury in 1872: “Ireland must be kept, like India, at all hazards: by persuasion, if possible; if not, by force.”

As prime minister, Asquith faced increasingly shrill demands to keep Ulster British. He was cajoled by the king and harangued by the Tory leader, Andrew Bonar Law. In truth, Ireland experienced two risings of competing movements for self-determination. Ulster unionism raised a force of 90,000 volunteers, established a provisional government in Belfast, and stood against the will of the House of Commons that had passed the 1893 home rule bill. Confronted by the threat of a mutiny in the army, the government eventually surrendered.

This Easter, a hundred years on, Ireland may at last be coming to terms with its complicated and contradictory legacy. There is a determination in the official commemorations to “remember, reflect and reimagine” by focusing on the future.

What about here in Britain? For those of us whose families hadn’t yet emigrated, making the short journey from Ireland to England or Scotland, the events of that Easter Monday are especially poignant. The anniversary offers a chance to reflect on the troubles of those who came, the discrimination they faced and how Britain is a better place because of Irish men and women of all traditions. However, in a nation where up to six million of us have a right to an Irish passport, there seems to be a reticence about marking the centenary of the Rising.

Perhaps it’s understandable. The imagery of an armed uprising in a capital city, even if it was a century ago, remains difficult. Those who took up German Mauser rifles at the GPO were a small group with competing motives, but they were worlds apart from those who took up the Armalite during the Troubles. The senseless horror of the Provisional IRA’s bombing campaign was a betrayal of the republican dreams of Michael Collins and Tom Clarke’s 1916 forces.

Today, many mistakenly confuse or wilfully conflate Irish with Scottish nationalism, when in truth they are opposites. Contemporary Irish nationalism is about leaving the UK and instead sharing an alternative island union, while Scottish nationalism is about leaving the UK and an island union to join nothing.

As for the minority of unionists in Britain who still have a 1920s instinct of “Ulster will fight and Ulster will be right”, let’s hope they finally put that sentiment beyond use. And those on the British left who ­approach the centenary commemorations with a “Troubles” mindset need to grow up. So much has changed because of the painstaking process led by Tony Blair.

One final thing. Maybe dust down those grandparents’ birth certificates and apply for your Irish passport. Do it with a relaxed sense of pride in having a modern dual identity. After 23 June, it might also be the one certain way to remain an EU citizen.