'I still feel a large degree of culpability'

As a boy growing up in the countryside outside Derry, Ivan Cooper would go down to the river Faughan and skim flat stones across the water. When the bullets started ricocheting along the ground on Bloody Sunday, this was the memory that came rushing back to him. "Who would have thought it? The mind does strange things at moments like that," Cooper reflected last week, standing at the very spot in Derry where the tragedy unfolded before his eyes 30 years ago.

At the time, Cooper was the SDLP MP for Mid-Derry – not a Westminster MP but an MP in the Stormont Parliament of Northern Ireland. He was a political oddity: a Protestant who had taken up the Catholic cause of civil rights in Derry in the late 1960s. He was one of those who organised and led the fateful march on 30 January 1972. "It was a horrific day," he says, "Even now I still feel a large degree of culpability."

Cooper, now 58, is a big, eloquent man with a warmth towards others that has survived the trauma he suffered – not just on Bloody Sunday but in the years of troubles that followed when there were numerous attempts on his life. Married with two grown-up daughters, he still lives in Derry. He left politics in 1983, since when he has worked as a consultant, on tax among other things.

His role in the events that led to the fatal shootings of 14 protesters in total by the Army is central to the long-awaited film Bloody Sunday, to be shown this evening on ITV. In the film, Cooper, then aged 28, is played by the rather older-looking James Nesbitt, best known for the comedy-drama Cold Feet. The film, written and directed by Paul Greengrass, is an extraordinarily vivid work, its documentary style so effective that you barely notice that you are watching acting.

That the Army does not come out of it well is inevitable. But the film succeeds in taking the viewer right inside the seething minds of both the paratroopers on the ground and the superior officers in HQ who were trying to control the march as it spilled over into rioting.

"It's a film of tremendous integrity," Cooper says, "and I admire it for that. I wouldn't have gotinvolved if I had not been convinced that it would do justice to Bloody Sunday, and I believe Paul has produced as accurate a portrayal as you could get." Nesbitt, with whom Cooper worked closely in the making of the film, "has done a remarkable job of capturing a character as diverse as me".

Cooper's destiny was carved out when as a young man he took a job in one of the shirt factories that were the industrial pride of Derry. When it came to religion, the workforce was integrated – "Derry has never suffered from the sectarianism you find in Belfast," Cooper remarks – but what he had brought home to him was the blatant disenfranchisement of the city's Catholics, two-thirds of the population, by the Protestant-dominated local council.

"I was a crusader, an idealist," Cooper says. "I went into politics as a Protestant who believed in working-class representation." If only it could have been that simple. As a champion of civil rights for Catholics, he was seen by his fellow Protestants as a traitor.

The first civil rights marches took place in 1968. Over the next few years, many of the movement's demands were met. But the IRA mobilised, the British Army moved in, and the highly contentious issue of internment without trial forced the authorities to seek a ban on marches. Nevertheless, Cooper and the movement he helped galvanise – avowedly non-violent, he maintains – would not go away. When Bloody Sunday resulted, it was a recruiting sergeant for the IRA and exacerbated violence that continued for 25 years.

What Cooper says he wants from the Saville Inquiry into the affair is a "complete declaration of innocence on the part of the protesters". But whatever happens, "to this city, even among the most moderate people, Bloody Sunday is a ghost that will always be there".