A judge has said he would not have recommended two drug-smugglers be freed from jail if he had known details they gave of hidden guns had been bogus.
Judge David Lynch told Southwark Crown Court he had sentenced the pair to 18 years in jail at Liverpool Crown Court for smuggling heroin in August 1995.
John Haase and Paul Bennett were freed under a year later after giving alleged false details about a large arms cache.
Both deny conspiracy to pervert the course of justice.
Judge Lynch said: "If I had been told by anybody that any part of this information was suspect, it would have thrown into doubt all of it, and I would not have reduced their sentences."
He added that the scale of apparent information they provided at the time was "unique" in his experience.
London's Southwark Crown Court heard the information from the pair resulted in 28 seizures involving an "awesome array" of 150 weapons, including grenades, and 1,500 rounds of ammunition.
Drugs, stolen property and fake Semtex were also recovered.
But jurors have been told it was all part of a plot the men put together from behind bars with the help of mobile phones.
According to prosecutor Gibson Grenfell, QC, they hoped the allegedly bogus hauls would win official gratitude and a reduction in their lengthy sentences.
Judge Lynch, who retired three years ago, said when the case came to Liverpool Crown Court and both pleaded guilty to drug smuggling, he had no doubt their help deserved recognition.
However, he was aware because of the highly sensitive nature of the information the men had given, that their lives "would be at risk" should their informant status become public knowledge.
The judge told jurors that having jailed the men for 18 years in open court, he wrote privately to the then Home Secretary Michael Howard, inviting the exercise of the Royal Prerogative of Mercy.
Once time already served had been taken into account, his suggestion of alternative five-year terms resulted in both men being released just 11 months later.
Haase, 59, and Bennett, 44, of no fixed address, Haase's wife Deborah, of Teynham Avenue, Knowsley Village, and Sharon Knowles, of Wadeson Road, Walton, all deny conspiracy to pervert the course of justice.
Deborah Haase also denies one charge of possessing illegal firearms and one of possessing illegal ammunition.
The trial continues.