Details of Sir John Hackett's dealings with David O'Connell, the man credited with introducing the car bomb to Northern Ireland, are contained in a file released to the National Archives in Kew under the 30-year rule.
The secret exchanges culminated in the IRA leader attempting to reopen direct peace negotiations with the British government, a year after the collapse of face to face talks between the two sides.
Sir John, by then retired and principal of Kings College, London University, had been the commanding officer in Northern Ireland in the early 1960s. David O'Connell had been active in the IRA's unsuccessful border campaign which was abandoned in 1962.
General Hackett contacted the Northern Ireland Office in September 1973 initially to warn of a plan he had heard about to assassinate the prime minister, Ted Heath, during a visit to Ireland later that month.
He met Philip Woodfield, the deputy under-secretary of state, who himself had a secret meeting with Mr O'Connell and Gerry Adams in a house on the Donegal border the previous year.
Mr Woodfield's record of the meeting, however, betrays his surprise at the nature of Mr O'Connell's relationship with General Hackett which he disclosed. "It appears that they discuss IRA tactics from time to time," he recorded.
"For example, the general said that a little while before the bombs were planted in London ... O'Connell asked him what he thought of putting car bombs in Whitehall. General Hackett advised him against this but very shortly afterwards bombs were set off in various parts of London." The exchanges had been going on for 15 months by then.
Despite being discouraged from further contacts, General Hackett sent a lengthy letter to the secretary of state, Willie Whitelaw, passing on what intelligence he had gleaned.
Mr O'Connell, he wrote, is "losing ground to younger and more impatient operators. To arrest him and remove him from the scene would loosen restraint on those and open the way for more irresponsible action."
They spoke several times on the telephone. "I offered my opinion that at some stage the Provisionals would have to brought in," General Hackett recalled. "They represented too deeply entrenched a body of opinion in Ireland to be wholly disregarded."
Whitelaw, who had sanctioned secret talks with the IRA leadership the previous year at a house in Chelsea, was appalled. He was convinced fresh contacts would result again in what he perceived as having been a political disaster.
In an internal note in October 1973 Whitelaw recorded: "My own view is that these documents are damaging in the extreme to JH [Hackett] and probably dangerous. O'Connell will probably let him down as he did me.
"If any of this became public, JH would be hounded in England as almost a traitor, certainly as helping the Queen's enemies. Not a good position for a general. I must be able publicly to stand as not accepting this line of action in any way if things get out. Perhaps I am too alarmist?!!!"
His letter to General Hackett a few days later was firm but polite. "I appreciate your wish to tell me of these exchanges but ... I hope that both I personally and my officials have made it absolutely clear to you that her majesty's government will in no circumstances negotiate with the IRA."
