The "worried" commander of Paratroopers who killed 14 civilians on Bloody Sunday was berated by his boss for not pushing harder into the Bogside no-go area, even though it would have led to more deaths.
The revelation is made by General Sir Mike Jackson, the former head of the British Army, in his newly published autobiography.
He reveals that in the aftermath of the 1972 killings, Brigadier Frank Kitson "brutally" told Col Derek Wilford that having got so far, he should have pushed on to "sort the whole bloody mess out".
Jackson, who was then adjutant to Wilford and had been by his side on Bloody Sunday, says his boss was feeling "bruised, battered and worried about what had happened in Londonderry" when Kitson came to see him in Belfast.
At the time Kitson was one of three regional brigade commanders in Northern Ireland but Jackson describes him as "the sun around which the planets revolved, and he very much set the tone for the operational style".
Brigadier Kitson (later General), described as an incisive military thinker, had written a book called Low Intensity Operation, detailing techniques to deal with insurgents and guerrillas, based on his experiences in British colonies including Cyprus and Malaya.
Jackson recalls greeting Kitson before ushering him to see Col Wilford and leaving the two alone.
"Though Frank Kitson was a brusque man, he knew his soldiering. He would have understood that Derek Wilford was feeling bruised, battered and worried about what had happened...
"Kitson has a very distinct nasal voice, so it would have been difficult not to overhear what he was saying even if I had been trying not to."
He says Kitson began: "'Well Derek, you'd better tell me what happened'. So I heard the Colonel describe the snatch operation across the containment line into 'Free Derry'.
"Kitson was generally supportive, but when Wilford had finished, he offered a trenchant comment. 'What I don't understand is why, having got that far in, you didn't go on and sort the whole bloody mess out'."
Jackson adds: "Kitson expressed himself pretty brutally, but he had a point. There was no doubt that we could have gone on to retake the 'no-go' area, though this would almost certainly have resulted in more deaths."
The former Army chief tells of his own shock and "worrying feelings" when it emerged just how many people had been killed by paratroopers that Sunday.
He says: "I was deeply shocked because, although the British Army had shot a number of persons in the past, there had never been deaths on this scale.
To this day it remains the most tragic such episode in the whole sad history of the Troubles.
"I was left with some very mixed and worrying feelings...I hated the thought, as some commentators would state straight away, that our soldiers might have lost control.
"I found it difficult to accept that there could have been any mass breach of discipline."
General Jackson, who gave evidence to the Saville Inquiry, said he had " no doubt we came under fire" but added the question remains " whether the response of some of our soldiers was proportionate or not".
? Soldier: The Autobiography - General Sir Mike Jackson, published by Batam Press, £12.99.