The dispatch - sent from the US embassy in Tripoli before the release of Abdelbaset Ali Mohmed al-Megrahi in August 2009 - reports the view expressed by the British ambassador at the time, Sir Vincent Fean. He is now the Consul-General in Jerusalem.
According to German news magazine Der Spiegel, provided with prior access to the 250,000 US Embassy cables obtained by the whistle-blowing website, Sir Vincent was said to be relieved at news the Scottish Government was intending to release Megrahi as he was suffering from terminal cancer and expected to live less than three months.
The cable said: "The British ambassador expressed relief that Megrahi likely would be returned to Libya under the compassionate release programme. He noted that a refusal of Megrahi's request could have had disastrous implications for British interests in Libya. 'They could have cut us off at the knees, just like the Swiss'."
The ambassador's comment on "the Swiss" is a reference to Libya's reaction after Swiss police arrested Colonel Gaddafi's son, Hannibal, and his wife, Aline Skaf, on charges of abusing servants in a luxury hotel. Although the couple were quickly bailed and the charges dropped, Libya responded by withdrawing billions of dollars from Swiss banks, cutting off oil supplies, denying visas and recalling diplomats.
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If accurate, the cable is evidence that the British government was clearly supportive of the decision by Scottish Justice Secretary Kenny MacAskill to release Megrahi, the only person convicted of the bombing of Pan-Am Flight 103 and the murder of 270 people. At the time, then prime minister Gordon Brown refused to comment on the decision and insisted the UK government had played "no role" in the release.
The question of whether the release was linked to trade deals is now the subject of an inquiry by the US Senate.
Last night Susan Cohen, whose daughter, Theodora, was killed in the bombing, said: "This (the cable] backs up what we have been saying that Megrahi was not released on compassionate grounds … that this was about business and I think it's despicable. Scotland said there was no pressure and obviously there was pressure."
Dr Jim Swire, whose daughter Flora was killed in the bombing, said the cable was bound to "re-light the question of whether pressure was put on Scotland by the UK government to get advantages for British governments in Libya".
A Foreign Office spokesperson said: "We are not going to speculate on any specifics."
A Scottish Government spokesperson said: "Megrahi is terminally ill with prostate cancer.The Scottish Parliament justice committee examined all relevant aspects of this issue, and concluded that the decision was taken 'in good faith'."