A secret meeting between senior members of the government and the SDLP four days before the Anglo-Irish Agreement was unveiled was described by Seamus Mallon as "one of the most moving moments he had ever experienced".

At the meeting in November 1985, the SDLP delegation, composed of John Hume, Seamus Mallon, Eddie McGrady and Joe Hendron, was brought up to date about the contents of the agreement.

There had been considerable tension within the SDLP, with some of the leading figures believing Hume had kept them out of the loop about what was going on. The meeting with the key figures from the Dublin administration was designed to put them all in the picture.

After saying the briefing represented one of the most moving moments he had ever experienced, Mallon added that he wanted to go beyond that.

“He would like to make it absolutely clear that he personally and his party would put their shoulder to the wheel and that Garret FitzGerald as taoiseach would not find him wanting. Nor would the Irish permanent minister (Peter Barry). Nor would those who take on the dangerous business of serving in the secretariat find him wanting.”

Michael Lillis, the senior foreign affairs official who took notes at the meeting, added that just as the dinner was breaking up, Mallon went on to say that as far as he was concerned, no matter who was in power in Dublin, it was the government which dealt with the Irish nationalists outside of Ireland, including the United States.

He went on to thank FitzGerald for the direct and full way he had treated the SDLP.

This was a clear reference to the fact that Fianna Fáil's Charles Haughey, then leader of the opposition in the Dáil, had dispatched his foreign affairs spokesman Brian Lenihan to the United States to lobby leading Irish American politicians to oppose the Anglo-Irish Agreement.

Mallon had served in the Seanad in 1982 on the nomination of Haughey and was widely regarded as being close to Fianna Fáil and suspicious of Fine Gael.

Persuading Mallon to back the agreement was one of the government’s priorities.

At the meeting, he told FitzGerald there were things about the agreement that he liked and things he didn’t like, but he pledged not to attack the Irish government and reserve his criticism for Downing Street for the failure to give enough in certain areas.

At the end of the talks, Hume concluded by saying that FitzGerald and his colleagues had included him and his three colleagues in the detail of the most secret negotiations between the two governments in a way which the SDLP found to be extremely impressive.

“It was a very new development. For the first time our people have been treated with total confidence,” Hume said.

The papers also reveal the depth of the tensions between Hume and Mallon, who feared loyalist assassination attempts on party figures involved in the Anglo-Irish Agreement.

An eight-foot fence was being erected around Mallon’s house when Irish official Dáithí Ó Ceallaigh visited him at home to discuss the political situation in May 1985.

Mallon was “deeply critical of John Hume”, Ó Ceallaigh recorded.

“He is very concerned about his own security. While I was in his house an eight-foot-high fence was being erected around his house. When he went to church last Sunday for his usual Mass, it was surrounded on all sides by the British army.”

Mallon had been informed that the soldiers were there to protect him, Ó Ceallaigh wrote. “They had received a tip-off that a loyalist group were out to assassinate him.”

Ó Ceallaigh met Mallon again in July 1985 and noted that “he deeply distrusts Hume”.

A secret document prepared by Ó Ceallaigh outlined details of a meeting with Mallon in October 1985, about three weeks before the agreement was signed.

Mallon expressed fears about “loyalist assassination attempts on prominent members of the SDLP, including himself, and on those people in Dublin who are believed to be involved in implementation of an agreement”.

Mallon stressed the importance of a united nationalist approach to reaching agreement. "He is fearful that if it goes wrong, constitutional nationalism in Northern Ireland will be destroyed," Ó Ceallaigh wrote.

“He is somewhat concerned about what Hume has in mind when he refers to an agreement helping to produce reconciliation. He suspects he may have devolution in mind.”

Mallon did not believe devolution was a possibility because he thought unionists would never accept powersharing, Ó Ceallaigh said.

Meanwhile, a report on the SDLP annual conference in November 1985, compiled by the Department of Foreign Affairs, recorded the delegates’ reaction to Hume and Mallon holding hands aloft on stage.

“It received a standing ovation, many delegates being visibly moved by the sight of the leader and deputy leader standing hand in hand as they acknowledged the tumultuous applause,” the report said.

The gesture of holding hands had been agreed between the two men in advance, the report stated.

Mallon was not the only SDLP politician to feel excluded from what was going on. At the end of May, McGrady told a Department of Foreign Affairs official that he had real difficulty judging what was happening in the talks since he had no information on the detail and had not been briefed by the party leader.

“He was particularly surprised that John Hume had not brought him into his confidence on at least some of the detail of the talks,” the official wrote.