A judicial review has begun over the decision to exclude the former Kincora boys' home in east Belfast from a child abuse inquiry being held at Westminster.
A victim is taking legal action to force an independent inquiry with power to compel witnesses and the security services to hand over documents.
Gary Hoy was abused by two men who were subsequently convicted.
There have been allegations that a paedophile ring at Kincora was linked to the British intelligence services.
The government has so far refused calls for the abuse scandal at the Belfast home to be included within the scope of the inquiry established by Home Secretary Theresa May and headed by New Zealand judge Lowell Goddard.
The government has said that as child protection is a devolved matter, the right place for the Kincora allegations to be examined is Northern Ireland's Historical Institutional Abuse Inquiry, which has been sitting in Banbridge.
The victims of Kincora claim the Northern Ireland inquiry lacks the powers to compel evidence or witnesses from government agencies.
Amnesty International, which is supporting the victims' legal challenge, says two military intelligence officers have alleged that the security services blocked police investigations into the child abuse at Kincora in the 1970s.
The judicial review is expected to last several days.
Three senior care staff at Kincora were jailed in 1981 for abusing 11 boys.
At least 29 boys were abused at the home between the late 1950s and the early 1980s.
One of the men who was later convicted, William McGrath, is believed to have been an MI5 agent.