Taoiseach Charles Haughey ordered a special investigation after it emerged via a Ulster Volunteer Force (UVF) warning that British intelligence wanted him assassinated.
The chilling UVF letter also claimed that the British secret service also wanted to use the Loyalist paramilitary group to help destabilise the Republic's economy by introducing such deadly diseases as anthrax, foot and mouth disease (FMD), and swine fever.
A letter, sent to Mr Haughey on August 5, 1987, claimed to be from a senior UVF official.
It revealed that allegations British intelligence was behind a dirty tricks campaign against both the Republic and senior Irish politicians were correct.
Charles Haughey’s old yacht, the Celtic Mist, at Dublin’s Grand Canal Basin yesterday. Photo: Fergal Phillips
"MI5, MI6, assisted by the SAS, used our force 1972 to 1978 and 1985," it warned.
"We killed 17 men on information supplied by British intelligence [but] MI5 were double crossing us all the time we were working with them."
The UVF warned Mr Haughey that British intelligence had wanted him dead.
"He [British intelligence contact] asked us to execute you, and supplied us with the following details. Your cars, aerial photographs of your house, your island home on the Kerry coast ... details of your trips into Farranford (sic) private airport, photographs of your plane. Photographs and the details of your private yacht."
The UVF official said they were also offered spores of deadly diseases like anthrax and FMD to wreck the Republic's agri-food economy.
"They plan by doing so to destroy Eire economy and to make the Eire Government increase border security."
Signed in block capitals "Capt W Johnston", the name used by the UVF in all its formal statements, it closed with the line: "We have no love for you, but we are not going to carry out work for the Dirty Tricks Department of the British."
An attached memo from the Department of the Taoiseach confirmed Mr Haughey had been made aware of the letter and its contents.
"He [Mr Haughey] asked that [the Department of] Justice might let us know if they have anything to report," the handwritten memo said.