The stakes were nothing less than control of Fianna Fail, survival of the government and, perhaps, the rule of law. Changing one man's statement by deleting certain sections that damaged the prime government witness in the Arms Trial might have seemed justified in terms of Realpolitik. But the law was broken. It had the smell of a stitch-up. And it happened in the Department of Justice.

The evidence tampered with belonged to the head of Military Intelligence, Col Michael Hefferon. And it was done to protect the minister for defence, Mr Jim Gibbons. But it was all for naught. When Col Hefferon took the witness stand in the Four Courts he gave the evidence originally tendered to the investigating gardai.

Following that, prosecutions for the attempted illegal importation of arms collapsed against Mr Charles Haughey, Capt James Kelly, Mr John Kelly, a Belfast republican, and Mr Albert Luykx, a Belgian businessman. Earlier, charges against a former minister, Mr Neil Blaney, had failed for lack of evidence.

The "doctored" statement may not have led to a miscarriage of justice, but some interests were clearly determined to do what was possible to load the scales in the Government's favour.

It would appear from documentation that has become available under the 30-year rule that changes to Col Hefferon's original statement were made within the Department of Justice on the authorisation of the secretary, Mr Peter Berry. His initials appear on the original document, as do instructions to "delete" certain key words and paragraphs. In all, 16 deletions were made, some relatively unimportant, that had a bearing on Mr Gibbons's evidence.

The most important one stated: "It is my opinion that Mr Gibbons knew that Capt Kelly was involved in assisting the Defence Committees in the North to procure arms."

The minister had insisted in court that he had no knowledge of such matters, but was finally driven to accept that he had "vestigial knowledge" but had never authorised such attempts.

The original statement from Col Hefferon, found by Capt Kelly in papers released by the Department of Justice last January under the 30-year rule, carries an official departmental stamp and a notation that the document was seen by the minister for justice, Mr Des O'Malley, on June 1st, 1970.

Contacted at his Dail office yesterday, Mr O'Malley said he had no recollection of the document and knew nothing about it. He declined to make any further comment until he had viewed the programme.

The content of Col Hefferon's statement was altered before it emerged as part of the Book of Evidence prepared by the attorney general, Mr Colm Condon SC. The deletions were such as to minimise Mr Gibbons's apparent knowledge of Capt Kelly or of his involvement in attempting to import arms. Mr Condon told the programme he never had sight of the original document.

The Arms Trial of 1970 was a departure point for Mr Jack Lynch and his government as he sought to direct militant nationalism into democratic channels. The resignation of the minister for justice, Mr Micheal O Morain, and the sacking of Mr Charles Haughey and Mr Neil Blaney a few days later, galvanised the country.

It was followed by criminal charges against the two ministers and the arraignment of Capt James Kelly, Mr John Kelly and Mr Luykx on charges of attempting to illegally import arms.

The choice presented by Mr Lynch and his supporters was between the gun and democratic politics. And, as the North edged towards conflagration and the establishment of the Provisional IRA, they put their militant colleagues in the dock to prove how serious they were.

Corners had to be cut and lies told to secure their objectives. And they were. At the end of the Arms Trial few believed Mr Gibbons to be a credible witness. And Mr Lynch's lapses of memory were almost as damaging to him as his earlier obvious failure to control his colleagues within cabinet. But the alternative was even bloodier conflict in Northern Ireland and the possibility that the whole island might be engulfed.

Col Hefferon told gardai he had advised Capt Kelly: "He could not as a serving Army officer become involved in the purchase of guns, but if he wished to become involved he would have to resign from the Army. . . He felt, however, that he would be acting dishonourably if he did not assist them."

The same conflict and violent emotions had been released within cabinet. The Arms Trial brought affairs to a head when the rule of law was set against nationalist emotion. The altered statement shows the rule of law was got at on that occasion to secure a particular result. That attempt failed. And its failure strengthened the militants.

A few months later, however, they lost comprehensively at the Fianna Fail ardfheis when they challenged Mr Lynch's leadership.