A former agent has claimed that a senior Irish government official has been working for British military intelligence for more than three decades.
The claim has been made by ex-Force Research Unit (FRU) agent known by the pseudonym Sam Rosenfeld.
Mr Rosenfeld says he worked for British military intelligence on both sides of the border during the 1990s.
Now, for the first time, the former agent has revealed that a senior Irish government figure is a current British military intelligence asset.
He also revealed that he has visited the Dail in Dublin as a guest of the man, whom he refused to name.
"I will tell you what they (British military intelligence) are super, super, super, sensitive about, they have somebody still working, and I am assuming there's many still working in the Irish Republic, but one of them holds a very senior position in the Irish government," he said.
Mr Rosenfeld added that he recently "looked and and they are now even in a (more) senior position than they were previously and they still work for the British government, ie, the army.
"So they are still at it," he said.
He said that he was aware of other agents from his time working undercover in the north and that they have either "moved on, given up....or they have moved into stronger and better positions".
Mr Rosenfeld said he is unaware of how the alleged agent at the heart of the Irish government was recruited.
"I don't know how the contact between the two came about," he said.
"I have a suspicion, obviously a suspicion is never proof, I have a suspicion of how it came about and that relates to somebody who used to work at the British Embassy in Dublin.
"That person is in a very senior position now."
Mr Rosenfeld, whose relationship with the British army eventually broke down, said the agent's involvement is long term.
"This person has been involved for longer than all the crap that's has gone on between me and the army, so that relationship has gone on to bigger and better things," he said.
He suggested that while in some cases intelligence "engagements" can be short lived the alleged Irish government agent falls into a different category.
"I mean, the intelligence is only available for a very limited period of time, depending on what kind of context you are talking about," he said.
"It depends on how you acquire it and in what circumstances.
"But there are times when you have people and you leave people and you don't bother people and they stay in place and you only have contact every now and again, sometimes these are long term engagements and this person is still there."
Mr Rosenfeld also revealed that he was often asked to spy on Irish army bases in the south.
"So the British army had identified every single target including targets inside the Irish government, specifically inside the military," he said.
"This is military bases in the Irish republic. I visited military bases and a few other places.
"Everything I done north and south of the border was under their (British army) direction and supervision."
The former military agent said that while Ireland poses no threat to Britain he believes there would be little the British government would not know about the affairs of their Irish counterparts.
"I don't think there's anything that the Irish government would have secret from the British government anyway," he said.
"It doesn't have the military prowess if you like, it's not a Russia, it's not a China, it's not really a potential enemy in any way shape of form but they would have stability and security and intelligence interests in what Ireland does."
He also said British intelligence analysts will be keeping a close eye on future political developments, particularly if Sinn Féin rise to power as current opinion polls indicate.
"I can guarantee you now that they are sitting there in their little war rooms planning out what will happen if Sinn Féin won in the Irish republic," he said.
"The dynamics of politics in Northern Ireland are shifting....people need to know what would happen if Sinn Féin were to suddenly have a majority vote or whatever in Northern Ireland and how the game would look.
"The British government would have a really, really, really keen interest in what's going on."