AT 10.40pm on May 5 1976 SAS soldiers Illisoni Ligairi and John Lawson were stopped at an Irish army/Garda checkpoint on the Flagstaff Road between Newry and Omeath.
The SAS men, driving a Triumph 2000 and in civilian clothes, were armed with two Browning pistols and two Sterling submachine guns.
They claimed they had strayed 700 yards into the Republic after misreading a map. They admitted being soldiers but denied being SAS and said they were off-duty test-driving a car.
However, when arrested Ligairi said: "I cannot tell you the mission we were on."
Four hours later six more SAS men in two cars were arrested at the same checkpoint after also "misreading" their maps.
All six were heavily armed, the weaponry including a pump-action shotgun and a dagger. They refused to hand over their weapons until their cars were surrounded by Irish soldiers.
The next day all eight appeared at the Special Criminal Court in Dublin on charges of possession of fire-arms without certificates with intent to endanger life.
The charges carried a maximum sentence of 20 years imprisonment.
Each man was released on £5,000 bail and allowed to leave the state.
The arrests came at a time when allegations of security force involvement in attacks in the Republic were at an all-time high.
Former British army intelligence officer Fred Holroyd would later claim that Captain Robert Nairac, who operated undercover, had admitted taking part in the murder of IRA man John Green at a farm in Castleblaney in the Republic in January 1975.
Confidential government papers now reveal that the SAS soldiers were questioned about three people found murdered in suspicious circumstances in the Republic at that time.
One of those was forestry worker Seamus Ludlow, whose body had been found near Dundalk four days before the SAS arrests.
The report recently published by Mr Justice Henry Barron confirms that the SAS soldiers were also questioned about the Dublin Monaghan bombings that killed 33 people in 1974.
However, the actions which the British government took to avoid its soldiers being imprisoned during the three weeks that followed their arrest can only now be revealed.
The new information is contained in previously unseen official British documents which had been kept from public view for 30 years.
In a telex message to the Foreign Office in London on May 7 British ambassador in Ireland Sir Arthur Galsworthy wrote: "One aspect of the defence that will need careful handling is the inclusion of a shotgun and what has been described as a dagger among the weapons carried.
"This was picked on by the minister for foreign affairs (Garret FitzGerald) and tends to be highlighted in the press here in an emotive way: And at some point we shall probably need to brief the defence lawyers very carefully about the use of these weapons.
"FitzGerald's understanding was that the DPP had felt compelled to institute court action because of the very unconventional nature of some of the weapons found (daggers and a sawn-off shotgun) and the fact that six of them were in civilian clothes; and the suspicions inevitably around the fact that the two groups had told different stories and that both differed from the preliminary account I had given to Keating (Irish Foreign Affairs official) that morning based on the information available to us at that time."
However, as it became clearer that the SAS men were now likely to stand trial attitudes in the British establishment hardened.
Confidential minutes of a May 12 meeting in London involving senior Foreign Office, Ministry of Defence and Northern Ireland Office officials, report Galsworthy as stating: "There was only one thing he could think of which would impress the Irish government.
"This would be for [Her Majesty's Government] to suggest that all British security forces be withdrawn to a line, say, 10 miles from the border.
"The buffer zone thus created would become a no-man's land in which the terrorists could do what they would."
Seven days later Galsworthy reported that he had warned Mr FitzGerald of the "appalling consequences that would follow if the case resulted in prison sentences".
Revealing that he had met Irish minister for justice Patrick Cooney that morning to discuss the charges against the SAS men, Gals-worthy stated: "When I laid on thick what an appalling effect a prison sentence would have, Cooney said that this was about the last thing in the world he as minister for justice would want.
"As my time with Cooney was very limited (he had to leave for a government meeting) I was unable to probe him about his remark that the matter of the prosecution is now out of the government's hands and to explore with him whether the attorney general can in practice lean on the DPP, eg to drop the first charge."
However, the lengths which the British government was prepared to go to so as to ensure the SAS soldiers did not stand trial were revealed in a letter to TF Brenchley in the Cabinet Office, dated May 18, from senior Foreign Office official GW Harding.
"You will know that the prime minister has said that, if the SAS men facing trial in Dublin receive prison sentences, he will wish to consider what we can do to bring home our displeasure to the Irish government and that he has asked for a contingency plan to be prepared setting out possible courses of action in this event," Harding wrote.
"There is a considerable range of more or less drastic sanctions which could be taken against the Republic.
"They include an embargo on trade, a ban on remittance, withdrawal of social security benefits from Irish citizens, prohibition or limitation of Irish immigration and the ending of the voting rights of Irish citizens in this country."
Warning that the sanctions would be subject to the possibility of "retaliatory action", Harding wrote: "There are some more modest steps which might fit the contingency more appropriately.
"They include a sustained campaign in the media against Irish 'failures' in security matters (eg extradition), a suspension of ministerial and/or official contacts with the Irish on Northern Ireland matters and a refusal of training and other facilities to the Irish security forces."
He again warned that such measures would "put at risk our security cooperation with the Irish".
He concluded that Britain's response to the SAS men being jailed "must be both firm enough to satisfy public opinion in this country and yet tempered by the need to limit the consequent damage to North/South security co-operation.
"This may point to a short, sharp reprimand, rather than a more protracted rebuff."
However, in a hardening of positions, a senior MoD official wrote to the secretary of state, Merlyn Rees, on May 25 stating: "I feel it would be naive to believe that in effect a prison sentence would not be something approaching a death sentence.
"Given the extent to which the Irish believe their own propaganda, and the mythology surrounding the SAS in the Republic, I can see little chance that the soldiers, were they convicted and sentenced to imprisonment, would escape uninjured."
In an interesting reference to the fact that the British establishment was already fully aware of attacks on six Irishmen wrongly convicted of the Birmingham pub bombings the previous year, he wrote: "One has only to think of the incident in this country in which those responsible for the Birmingham bombing were assaulted by prison officers to realise how much more likely a similar, or probably more serious occurrence would be in this case.
"Obviously, we must give full weight to our relationship with the Republic of Ireland, but I cannot help feeling that the Foreign Office have been concentrating on this to the exclusion of common sense.
"This is not purely a matter of international relations; it could have serious domestic repercussions, and I am naturally inclined to attach greater significance to these, particularly in so far as they affect the army itself."
In one of the most serious incidents the Northern Ireland Office discussed an app-arent attempt to coerce the Republic's DPP into dropping the charges.
A confidential memo written by NIO officials, dated May 24, said the DPP "might be susceptible to covert persuasion by the Irish government but since he is newly appointed and this may be seen as a test case of his independence the chances are slight and certainly nil if there is any overt indication that he is giving way to political pressure.
"There should certainly be advantage in bringing the Irish government to seek to apply effective persuasion to the DPP but there is some risk that they might mishandle the matter."
Warning that it would be "counter productive" for the British to be publicly exposed to have pressured their Irish counterparts into "leaning on" the Republic's DPP, the NIO memo stated: "We must be extremely careful not to appear to be pressing the Irish government to influence the DPP.
"We should however, impress upon them that HMG is not prepared to run any risk of its soldiers going to jail for map reading errors particularly when their safety cannot be guaranteed.
"The full consequences for the political and security situation, north and south, must be spelled out to the Irish since, unless the direct embarrassment to them of their actions is clearly shown, they are unlikely to act to safeguard the UK interest alone."
Warning that the Irish government needed to be "disabused" of the belief that reducing the charges to a fine would be acceptable to the British, it stated: "If we fail to persuade the DPP to offer no evidence then we should immediately press the Irish government for the guarantee in advance of a free pardon by the president or at least full remission of penalties."
On May 24 briefing notes drawn up for secretary of state Merlyn Rees for a meeting with British prime minister James Callaghan and the Labour cabinet warned of the potential for loyalist violence if the charges against the SAS were not dropped: "In Northern Ireland it could provide the catalyst that would bring the loyalist groups together and create a situation of considerable instability.
"There could also be a strong and violent reaction by loyalist paramilitaries."
Calling for the British to resist any extradition request from the Irish if the SAS did not turn up for trial, it stated: "It would be possible to give the men immunity from this process by means of legislation in the shape of a one clause bill.
"Moreover the attempted use of such questionable powers by the army authorities to send soldiers back to face prison sentence would have such bad effect on discipline and morale as to render it unthinkable."
The notes state that in the event of the Republic's DPP pushing the case to trial "ways must be found of avoiding the men appearing in court at all, and that contingency plans should be drawn up to provide immunity from any warrants issued by the Republic for the men."
Eventually when the eight stood trial in March 1977 they were cleared of the charge of possession with intent to endanger life and were each fined £100 on the lesser charge.
Speaking after the court hearing British ambassador Robert Haydon said: "We are very satisfied that the men have been acquitted of any ill-intent in the Irish Republic.
"We imagine that the fine was more or less mandatory and the Ministry of Defence will pay."
A Foreign Office spokesman was quoted as saying it was "very satisfied" with the outcome.
The following year the Irish government agreed that the British army could fly into the Republic if in pursuit of gunmen.
However, present Co Louth Sinn Féin TD Arthur Morgan said the new information on the arrests and release of the SAS raised "fundamental questions" about the incident.
"At this time at least four people were murdered in mysterious circumstances in the border area, including Seamus Ludlow and Peter Clancy in Louth," he said.
"Nobody was ever charged with these killings, although loyalists or elements of the British state were always suspected."
Mr Morgan said that he was alarmed at the apparent attempts to secure cooperation from the Fine Gael-Labour Irish government of the time to influence the case.
"I believe that these revelations will be the tip of the iceberg," he said.