The amount of money being used to pay confidential informants has increased by 33pc in the last five years.

Last year almost €700,000 was spent by the Secret Service, which is used to pay monetary expenses to Garda informants.

The section is maintained by both the crime and security branch of the Garda and the intelligence section of the Defence Forces.

The 2016 Appropriation of Accounts by the Comptroller and Auditor General shows that €684,000 was spent by the Secret Service last year. In total, €1m is allocated to the section annually, which includes the Covert Human Intelligence Source (CHIS) system.

The amount is up significantly from the €515,000 used by the unit in 2012, and the €587,000 spent in 2013.

The audit also states that €1.3m was used by the Garda’s Witness Security Programme last year. This programme, often referred to as witness protection, is controlled by the Garda’s crime and security section and was established in 1997 in response to gangland crime.