A documentary to be screened next Sunday will air suspicions that British intelligence had advance knowledge of an IRA attack in Holland, in which two Australian tourists died, but failed to stop it.

Stephan Melrose (24) and Nick Spanos (28) were shot dead by IRA gunmen, who mistook them for British soldiers, in Roermond 20 years ago. This month the Melrose family visited Holland and Ireland in their quest to find answers about the murders.

Award-winning investigative journalist Ross Coulthart accompanied them and his programme will be screened on Australia's Channel Seven. It includes a confrontation between the reporter and Gerry Adams who served on the IRA Army Council at the time of the killings.

Coulthart said: "Just after the shooting, an Australian source with good links to British intelligence suggested to me that the British had details of the IRA cell operating in Europe, that they had information on its key members, and that they could possibly have stopped the attack. This is supported by ex-British agents we've interviewed."

There is speculation that at least one, and probably several, members of the IRA team in Europe were informers. Coulthart said information from British intelligence sources also suggested that, at the most senior level, one in two IRA leaders were British agents. "The question must be asked whether two Australians were sacrificed to protect informants in the IRA," he said. Donna Maguire and Paul Hughes from Newry, Sean Hick from Glenageary, Co Dublin, and Gerard Harte from Lurgan were charged with the double murder.

Forensic and eyewitness evidence was presented in court. Despite what the prosecution believed was a strong case, only Harte was convicted and his conviction was overturned on appeal.

Four months before the Australians' murder, Maguire was acquitted in a Dublin court of possessing explosives and maps of a British army base in Germany.

Maguire, Hick and Hughes were later acquitted of the 1990 murder of a British army major in Germany. Maguire was also acquitted of a bomb attack on a British army base in Hanover but was convicted of the 1989 failed bomb attack on the Osnabruck base.