Secret royal pardons granted to NI paramilitaries
The government has admitted that royal pardons were given secretly to paramilitaries in Northern Ireland in return for information.
The cases date as far back as the 1980s.
But Northern Ireland Secretary Theresa Villiers said it would be wrong to name those granted a royal prerogative of mercy in terrorism-related cases.
Speaking on BBC Radio 4's File on 4, she said there was an argument for making details public in future cases.
Her comments follow revelations that royal prerogatives of mercy were used in 16 terrorism-related cases in the years immediately after the Good Friday Agreement.
However, Ms Villiers said it was impossible to give a total beyond that, because records for the decade leading up to the crucial peace agreement had either been lost or not kept.
"I can't give you information about that ten-year period, but prior to that ten-year period it may well have been that the RPM was used in relation to some terrorist cases," Ms Villiers told File on 4.
Questioned further, she said that there were several instances when pardons or prerogatives of mercy had been granted during Margaret Thatcher's time in government.
"It was used, for example, in cases where people might be released early on compassionate grounds," she said.
"It was also used in some instances, I understand, in exchange for information provided to assist the authorities in prosecuting other people - again to shorten sentences."
The royal prerogative of mercy, commonly known as a royal pardon, allows changes in sentences without the backing of, or consultation with, Parliament.
Northern Ireland First Minister Peter Robinson has called for the issue of royal pardons to be included in the judge-led inquiry into the On the Runs controversy.
On the Runs is the term used to refer to people who are suspected of, but who have not been charged or convicted of paramilitary offences during the Troubles.
It was a process that involved letters being given to republican paramilitary suspects assuring them that they were not wanted by police anywhere in the UK.
Details of the On the Runs scheme came to light after the trial of a man suspected of the IRA bombing of Hyde Park in 1982 collapsed in London earlier this year.
John Downey, from County Donegal in the Republic of Ireland, had denied killing four soldiers in the attack.
A court ruled that he should not be tried because of the assurance contained in a letter that he had been given in error by the government.
Informants who gave evidence during so-called supergrass trials are thought to be among the recipients of the pardons. However, Theresa Villiers indicated that some names and uses of royal pardons had never been made public.
"Throughout the debate on the past we do need to be careful about disclosing the identities of individuals," she said.
"We always have to bear in mind the importance of ensuring that we don't end up revealing information that can jeopardise life and limb."
When royal prerogatives of mercy are used in England they are printed in the London Gazette. However, RPMs are generally not published when they are granted in Northern Ireland.
Ms Villiers acknowledged that after the controversy over both On the Run letters and pardons, there was now an argument for the details of RPMs to be made public in Northern Ireland too.
"We are looking at that at the moment and I think there is a case for that," Ms Villiers said.
"I think that question though is somewhat different to retrospective publication of names from the past."
Northern Ireland's outgoing victims commissioner, Kathryn Stone, said: "When news of these comes out again in a kind of drip, drip, drip way, again it erodes the trust and confidence,
"But it is such a serious thing. And you start to move into Donald Rumsfeld territory don't you... There are things that we know, we don't know and there are things that we don't know, we don't know.
"And we don't know what else there is that's going to be revealed."
Ms Stone is due to leave her post later this week.
You can hear more on File on 4 on BBC Radio 4 at 20:00 BST on Tuesday 10 June.