Mr Grenfell said: "Cook was throughout the handler of their information and passed it on to Merseyside Police and other authorities as he judged appropriate."

Twenty-eight firearms seizures, sometimes of numerous firearms, were made on the strength of their information.

Scientific and other evidence demonstrated a considerable number of the firearms in those seizures came from just two sources, a man called Shaw and a man called Mitchell.

Haase and Bennett were able to make arrangements for the firearms to be put down so they could be found through the use of mobile phones and making contact with their accomplices outside prison.

Mr Grenfell said: "Contrary to normal prison rules, they had mobile telephones when inside prison and could and did make and receive calls whenever they wanted."

Deborah Haase and Knowles were allegedly among the accomplices, he added.

Deborah Haase was at that time Deborah Dillon, and later married Haase.

Mr Grenfell said the judge, when sentencing in August 1995, was told the lives of Haase and Bennett would be at risk if what they had done by way of providing information became publicly known.

"To preserve appearances and avoid any risk of them being identified as informants, he sentenced each of them in open court to 18 years’ imprisonment. However, he wrote privately to the then Home Secretary, Michael Howard, inviting consideration of the exercise of what is known as the Royal Prerogative of Mercy, suggesting that an appropriate sentence would be five years’ imprisonment. The Royal Prerogative was exercised and as a result both men were released on July 4, 1996."

Mr Grenfell said Haase and Bennett were the architects of the scheme to mislead the sentencing court.

Deborah Haase’s fingerprints were found on black bin bags in a car in one of the seizures, which contained firearms.

Knowles was linked to the seizures, he said.