In the hall of St Agnes's Church at Kennington Park in London, the events that occurred in Gibraltar on March 8th, 1988, have slowly been brought back to life. The episode is known as Death on the Rock, after a TV documentary that was, for many, the defining account.

Mairead Farrell, Danny McCann and Seán Savage had planned to massacre the bandsmen of the Royal Anglian Regiment with a car bomb at the changing of the guard outside the governor’s house in the British dependency. Instead, they died in a hail of SAS gunfire.

Next week, a new play will open in London. Titled Gibraltar , it focuses not only on the killings but on the media coverage and the varying narratives that survive. Today, despite an inquest, a European Court of Human Rights ruling and acres of newsprint, every second of their final moments remains deeply contested.

"The thing that most people remember about it is Thames Television's Death on the Rock programme," says George Irving, the actor who plays Nick Hammond, a journalist who becomes obsessed with discovering the truth about the day.

A local jury found the killings lawful, although the European Court of Human Rights found otherwise. At the same time it rejected calls for damages by their families, given that the three “had been intending to plant a bomb”.

For many, the defining witness was Carmen Proetta, a Gibraltarian woman who became a hate figure for the British tabloid press who crowded into the tiny British overseas dependency, pleased that the IRA had been dispatched by “Maggie’s SAS”.

Proetta said “a man and a woman” – McCann and Farrell – “raise their hands over their shoulders with open palms” but were shot by men who “jumped the barrier” that ran down the centre of the busy road.

Alistair Brett, who wrote the play, is a former Sunday Times lawyer who was deeply involved in contesting a legal action by Proetta. He disputes her recollections, arguing that others said the three were shot by soldiers who had been following them on foot. "They were not putting their hands up; they were not walking anywhere. It is uniformed coppers who jump out of the car, not the SAS," Brett says.

Brett’s interpretation of events could be controversial. Proetta secured a series of libel victories against tabloid and broadsheet newspapers.

In the febrile hours after the killings, the British position on them was vague, inconsistent and contradictory: the car bomb was already in place; it could be detonated by remote control; the three were armed.

“In the event, all of these crucial assumptions, apart from the terrorists' intentions to carry out an attack, turned out to be erroneous,” said the European court in its 1995 judgment, though it acknowledged that they were “possible hypotheses”, given the IRA’s history.

“The play tries to say you can’t be sure of any version of events, regardless of where it comes from,” says the director, James Robert Carson.

With few exceptions, the British press did not distinguish itself, argues Brett, who has drawn on the Guardian journalist Ian Jack's accounts of reporters singing "You can't kill an SAS man, he is Maggie's assassin" to the tune of My Old Man in pubs in Gibraltar.

Conspiracy theories abound about Gibraltar, and Brett has his own: that the IRA, which had seen the Eksund seized with its arms cargo the year before, had turned to drugs smuggling to refuel its coffers.

Low on funds, the IRA had embarked on its so-called Euro campaign. Before Gibraltar, it had injured 30 people in Rheindahlen, in Germany, when a 130kg car bomb exploded, and it had killed three RAF servicemen in attacks on Roermond and Nieuw Bergen, in the Netherlands.

“Gibraltar was supposed to be top secret. But did it leak out with somebody’s connivance, because they didn’t want X number of soldiers [killed], and there was an old people’s home next to the square and a kid’s school and because they didn’t want another horror story?” asks Brett.

“It would have done the IRA no good at all, so was it strategically done so that three heavyweight IRA terrorists were sacrificed on the altar of political expediency?” He believes the Gibraltar killings made space for the early negotiations that eventually led to the Belfast Agreement.

Gibraltar runs from Wednesday until April 20th at the Arcola Theatre in Dalston, London