But a detailed investigation by two respected reporters - one American, the other Australian - has concluded that Aspin was just that. The American, John Loftus, is a lawyer who has worked for the US Office of Special Investigations, prosecuting Nazi war criminals. His co-researcher is Mark Aarons, an award-winning reporter who worked for the Australian Broadcasting Corporation for two decades.
If they are right about Aspin, we will have to revise the generally accepted account of Britain's role in 'Irangate' - the secret and illegal plan to sell arms to Iran in return for its help in releasing American hostages in Lebanon - and in a series of covert wars in the Middle East during the past decade. This week their findings are published in the US in a book entitled The Secret War Against the Jews.
Britain has always denied involvement in Irangate. The architects of the scandal, chief among them Lieutenant-Colonel Oliver North (who worked out of the Reagan White House), intended to use the profits from arms sales to Iran to fund the Contra guerrillas in Nicaragua.
The world first learnt of Irangate through a Lebanese newspaper article in November 1986. President Reagan set up the Tower Commission to investigate.
It reported in February 1987 and lifted the lid on a world in which governments, intelligence agencies and terrorists worked hand-in-glove.
The British public was not unduly troubled by the scandal. There was no evidence that Britain had been involved.
However, on 1 May 1987, Leslie Aspin went to his solicitors and signed an affidavit in which he told a detailed story of his involvement with North.
He also claimed that the US was paying for it through the BCCI bank, which it knew was a centre for international money-laundering. He claimed that Ian Gow, the late Parliamentary Private Secretary to Margaret Thatcher, acted as the British government's representative in the deals. Aspin knew Gow well enough to have his unlisted telephone number.
The affidavit was impressive in its detail. For instance, Aspin quoted the number of an account at the Paris branch of BCCI in the name of Devon Island, one of the front companies used in Irangate. Loftus and Aarons say that Aspin could not have known such details unless he was working, as he claimed, both for the Reagan White House and for British intelligence.
The Tower Commission reported that the first arms sale to Iran took place in 1985 at the initiative of the Israeli government. Loftus and Aarons contend that the idea of trading guns for hostages was hatched in the office of Vice-President George Bush in 1984 and that the first sale took place in July that year. Aspin was the British involvement in the deal: he arranged it.
In his affidavit Aspin claimed he was contacted by William Casey, then head of the CIA, in June 1984. 'He requested me to assist in the sale of (arms) to Iran in exchange for hostages. These hostages were being held in Lebanon, so in June 1984 I started (attending) a series of meetings in London, one of them being at the US Embassy . . . During these meetings, it was discussed as to how one could get the hostages released, ways of doing it, some of them improper, some proper.'
Aspin also claims he regularly briefed and took instructions from Gow. The plan was to send a shipment of artillery ammunition to Iran via Greece, piggy-backed on a similar munitions shipment to the PLO. The shipment was intercepted by the Greeks after a tip-off from the Israelis, who did not know it had been sanctioned by the US government.
The key to Aspin's credibility is a claim that he met North to discuss more arms-for-hostage initiatives in Paris on 14 November 1984. North has always denied this. But Loftus and Aarons have, for the first time, been able to prove that on 14 November North was indeed in Paris. He flew to London on 12 November for a 'counter-terrorism' conference and left for France the next day.
They obtained this information by applying, under US freedom of information legislation, for copies of North's travel vouchers. They had been tipped off that he might have claimed expenses for the trip.
Aspin claims that during his meeting with North he was given BCCI account numbers into which the Americans would deposit money to pay for US TOW missiles that were being traded with Iran.
In the event, according to Loftus and Aarons, Casey got cold feet. He was worried that the TOW missiles could be traced and proposed sending the Iranians French STRIM missiles instead. But the Iranians refused to accept the French missiles; they wanted US ones. So Aspin set up another deal that did go through.
Claims of British involvement are not limited to Aspin nor to his briefings with Gow. Loftus and Aarons allege that a senior diplomat in the British Embassy in Washington at the time, Andrew Green, regularly met North. Green confirmed to the Independent yesterday that he had met North, but not to discuss Iran-Contra.
The US would have had good reason to involve Britain: London had excellent contacts with Middle Eastern drugs and arms dealers, who were well positioned to facilitate the Irangate trade. In particular, the British had recruited as an agent a notorious Syrian drug dealer, Monzer Al-Kassar, whom Aspin knew from the Seventies when they had been involved in gun-running.
Al-Kassar was responsible for the 1985 hijacking of the cruise ship Achille Lauro, according to Interpol, and had access to the kidnappers in Lebanon.
He eventually acted as the arms intermediary with the Iranians for Aspin and the Americans.
In return for their assistance, the British wanted information from the CIA on IRA fund-raising in the US. Aspin's motive for involvement is also clear: saving his friend Bill Buckley, the kidnapped head of the Beirut CIA station. The Americans were most anxious to retrieve Buckley. But the attempt to buy his freedom with arms failed. He was tortured to death in 1984.
Loftus and Aarons allege that in 1980 Aspin and Buckley had been involved in a secret commando assault on the Holy Mosque in Mecca after it was seized by Islamic extremists. The Saudi Arabians had asked the US to intervene. Loftus and Aarons have seen pictures, taken by Aspin, of a firing squad that executed the radicals outside the mosque. There is also a picture of Buckley and Aspin embracing after the raid.
Aspin first met Buckley in Angola during the late Seventies. Aspin was recruiting mercenaries to fight Communist guerrillas on behalf of the Americans, after Congress had outlawed aid to Angola. Buckley was there for the CIA.
Before that Aspin had been a soldier and served in the SAS. He then worked as an arms smuggler for Palestinian terrorists, and it was then that he got to know Al-Kassar. MI6 recruited him in 1970 - it wanted information on connections between Middle Eastern terrorist groups and the IRA.
In 1975, after a dispute with British intelligence, Aspin sought work with the Americans. He trained with US Special Forces and won a green beret. In 1978 he was offered a formal contract with the CIA - a copy of this still exists. In 1980 he engineered the release of two British hostages in Iran by supplying American weapons: this ransom deal was the prototype for Irangate.
Those who met Aspin describe him as tall, ordinary-looking, a loner. Yet Loftus and Aarons assert: 'There was more to Aspin than he let on. He was extraordinarily loyal to causes he believed in, as well as to friends and family. He was . . . bold, brash and very, very bright.'
Loftus and Aarons admit they were tempted to dismiss Aspin's story. What persuaded them was the extensive documentation corroborating his affidavit.
Aspin swore this affidavit when he knew he was dying. He concluded his statement: 'I would like to prefer that the British police continue to think of me as an idiot and a bit player in this whole affair . . . ' And then Leslie Aspin faded back into the shadows in which he had lived most of his life.