On 21 October 1966, the village of Aberfan in South Wales was devastated when a large coal-spoil tip collapsed and engulfed the Pantglas Junior School and several houses. The catastrophe killed 144 people, including 116 children.

Tip 7, a pile of colliery waste deposited on the hillside above Aberfan, had become saturated by heavy rain. The spoil liquefied and flowed rapidly down the mountainside. It engulfed the school and surrounding homes.

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The House of Commons met on 25 October to establish a tribunal of inquiry into the disaster under the Tribunals of Inquiry (Evidence) Act 1921.

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Wilson, moving the motion on behalf of the government, vowed the inquiry be “clothed with all the powers that it may need to get at the truth”. He acknowledged, however, that no action could “set back the clock” or restore “this bereaved community the loss of an entire age-group, practically all the children between 8 and 10.”

He added: “All we here today can do is to provide part of the means of reaching the truth, for that truth must be known.”

Edward Heath, the leader of the Conservative Party, voiced his support for the motion. He told the House that his mind was “still numb at the thought of the immensity of personal grief caused by [the disaster], and the irreparable blow which this small and closely-knit community has so suddenly suffered.”

On 27 October, the attorney general, Elwyn Jones, warned that public comments on those matters now under investigation by the Tribunal were “highly undesirable”. He warned that “such comments may have legal consequences which are, perhaps, not at present appreciated”.

Jones said there was a “danger in examination of potential witnesses on television and in the press”, maintaining that “the best means of ventilating opinion… if we are to get to the most effective result from this inquiry is by communication with the tribunal itself.”

The Aberfan tribunal report, published on 3 August 1967, placed the blame for the disaster squarely on the National Coal Board (NCB) for its negligence in the creation and management of the spoil tips. Tip 7 was found to have been built over known underground springs.

The inquiry accused the NCB of failing to act upon repeated warnings from local residents.

The tribunal report cited “a terrifying tale of bungling ineptitude by men charged with tasks for which they were totally unfitted, of failure to heed clear warnings, and of total lack of direction from above”.

The tribunal was also severely critical of the NCB’s conduct during the inquiry itself. The report noted that “much of the time of the Tribunal could have been saved if… the National Coal Board had not stubbornly resisted every attempt to lay the blame where it so clearly must rest – at their door.”

The disaster and report sparked public outrage against the NCB’s leadership, notably its chairman, Lord Robens.

Robens did not immediately go to Aberfan after the disaster; first he proceeded to Guildford to be installed as chancellor of the University of Surrey, arriving at the scene of the slip some 36 hours later.

The government also came under criticism for appropriating £150,000 from the Aberfan Disaster Memorial Fund (ADMF) fund to help clear the remaining tips.

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The report’s findings were considered by MPs on 26 October 1967. Cledwyn Hughes, the secretary of state for Wales, affirmed the government’s “general acceptance” of the tribunal’s recommendations.

Margaret Thatcher, the newly appointed shadow fuel and power minister, expressed concern about the NCB’s “complacency” following the publication of the tribunal report. Thatcher’s doubt stemmed from a Daily Telegraph report, dated 31 August. She quoted Lord Robens as saying: “At no time did anyone think of pit tips as that sort of potential danger.”

The shadow minister said she found this statement “extremely worrying” because the tribunal’s report contained “evidence upon evidence” contradicting it.

She referenced a specific exchange from the tribunal where a NCB board member and “tip expert”, W. V. Sheppard, asked if the board appreciated that tips could slide. “That was appreciated, that tips slide”, he responded.

The questioner, Thatcher relayed, then queried whether “it appreciated that when they do slide they can often slide a long way?”

Sheppard replied: “That was not appreciated, no.”

Thatcher said she was “absolutely astounded” at Sheppard’s ignorance.

She also raised the question of why A. H. Kellett, the chairman of the NCB in South Wales, had stayed in Japan for a conference during the fallout from the Aberfan disaster.

Richard Marsh, the minister of power, defended the decision to keep Lord Robens in post, describing him as a “superb leader of men”. Robens had offered to resign.

Marsh said that dismissing Robens would be a “gesture of a kind which would be virtually indecent.”

Marsh instead focused on the collective responsibility of parliament and society.

He told the House: “There is nothing that we can do for the people of Aberfan. Their children died as a result of the neglect of generations and the blindness of an entire nation. It is a blindness which has been shared in other countries.

“We can make no reparation for what has happened, and it would be an impertinence to try. When people have suffered as they have in Aberfan, there is nothing that anyone can do to help.”

Leo Abse, the Labour MP for Pontypool, described the rejection of Robens’ resignation as a “graceless pavane”.

The tragedy ultimately led to the passage of the Mines and Quarries (Tips) Act 1969, which introduced new regulations for the inspection and safety of spoil tips.

Ron Davies, the secretary of state for Wales, paid back £150,000 to the public disaster fund upon the change of government in 1997. No adjustment was made for inflation or the interest.