A round of interviews with former KGB agents had achieved what he had hoped for when he flew out the previous Sunday: corroboration of some extraordinary allegations contained in the manuscript of a book - Next Stop Execution - by the Soviet defector Oleg Gordievsky.
Only a tight-knit group of senior Sunday Times editors knew of Leppard's mission. When he returned, the button was pushed on their plans for a startling front page three days later.
"KGB: Michael Foot was our agent", screamed the Sunday Times headline, a prelude to three pages covering the KGB's targeting of Labour and trade union leaders from the 1960s to the 1980s. The paper reported that two former KGB members said the organisation had regarded Foot as an "agent of influence" and that, during his editorship of the left-wing Tribune newspaper in the sixties, he had accepted funds from the KGB.
That morning, the Foot story met a wave of derision and denial. John Witherow, the Sunday Times's editor, appeared to backtrack almost immediately, explaining on BBC radio that the paper was not saying that Foot had been a KGB agent (that allegation, he suggested, might be "utter rubbish"), merely that the KGB believed he was an agent. A subtle difference of course, but as one senior Sunday Times insider said yesterday: "If that's the case, then why was it splashed across three pages? If you go with a story, you don't say by Sunday lunchtime that you never believed it."
For sceptics, the story carried echoes of another famous Sunday Times scoop. Shortly before the 1992 General Election, the paper splashed its front page with a story about conversations between Neil Kinnock, the then Labour leader, and Soviet diplomats in London. The article consisted of accounts of meetings between Viktor Popov, the Soviet ambassador, and Kinnock during the miners' strike and cruise missile controversy.
The reality is that there was nothing peculiar in a Labour leader speaking with the Soviet ambassador and the story was quickly dismissed as a pre- election smear. To critics of the Sunday Times, the parallels between Foot's KGB and Kinnock's Kremlin connections were all too obvious - another bald attempt by the paper to malign the old enemy, the Labour Party.
The truth about how the Foot article came to appear has, however, less to do with political dogma than the new imperatives of the newspaper market. It is a story of how newspapers with copies to sell court book publishers with titles to hype.
Book serialisations have been something of a mixed bag for the Sunday Times. It was ridiculed over its purchase of the fake Hitler diaries in 1983 and vilified for serialising Josef Goebbels's genuine article in 1992, but the strategy paid off with Andrew Morton's Diana: Her True Story in the same year. Since then, the paper's quest for a title that could work the same magic for its pages and sales has taken on Holy Grail-like proportions.
The paper hoped that Oleg Gordievsky might provide the spark it needed. Ever since the former head of the KGB's London station defected in 1985, there had been fevered speculation about "Oleg's List" of UK contacts. The account of life as a double agent would not only read like a John le Carr novel, but would come appended with a "who's who" of the British political establishment he had cultivated on Moscow's behalf.
The publishers Macmillan commissioned Gordievsky to write a book in October 1993 and immediately newspapers began a feverish round of bidding for the serialisation rights. Last October, the Sunday Times obtained the manuscript but does not appear to have secured serialisation rights until December.
As with all high-profile serialisations, the Gordievsky project was overseen by a small team, which included Witherow and Richard Ellis, a senior news executive.
When the Sunday Times acquired serialisation rights, Gordievsky and Macmillan had not resolved whether they could run the risk of naming names. MI6 lobbied strongly for them to be left out, as did Macmillan, but it was the names that the Sunday Times wanted and in persuading Gordievsky to hand them over, it seems that cheque-book spoke louder than warnings.
The draft manuscript identified Michael Foot and Richard Gott, the Guardian's former feature and then literary editor, as agents, but the Sunday Times had only Gordievsky's word for it. The unmasking of Richard Gott by the Spectator in December underlined the need for the paper to move quickly. Although he described Gordievsky this week as "an extremely reliable source in the past. . . always accurate to an almost pedantic degree", Witherow said the paper would need corroboration: "There was never any serious doubt that what he was telling us was true, but it had to be substantiated."
That was where Leppard fitted in. On Sunday 12 February, he flew to Moscow, where, according to Witherow, he met half a dozen former KGB agents, including Mikhail Lyubimov, press attach to the Soviet Embassy in London from 1961 until he was expelled by MI5 in 1965, and Viktor Kubeykin, who ran the Labour party and trade union desk at the KGB's London station during the 1970s. It was there that a "sceptical" Leppard, Witherow says, became convinced that the KGB had regarded Foot as an "agent of influence".
Speaking in Moscow this week, Lyubimov appeared to be baffled by the conspiracy theories of the Sunday Times. As a Soviet spy in London and then in Moscow, as chief KGB desk officer for Britain from 1974 to 1976, he played a key role in the supposed KGB recruitment of Foot and other well-known figures in the Labour Party and trade unions as Soviet "agents of influence".
Lyubimov acknowledges meeting Foot for lunch in Soho under his cover as press attach in the Soviet embassy but denies channelling cash to support the impecunious journal Tribune. "I met hundreds of people. If I published a list of all my contacts in London it would be very, very long. The idea that Foot was any kind of agent is a ridiculous smear," he says.
Still angrier about the Sunday Times story is Viktor Kubeykin."They wrote the exact opposite of what I said. This a 100 per cent distortion."
He too admits to meeting Foot and other politicians but denies any knowledge of the Labour leader ever having the codename "Boot" or having provided any information or other services to Moscow.
All the same, Lyubimov and Kubeykin do credit the Sunday Times and its chief informer Oleg Gordievsky with exposing a plot of sorts - the way in which the KGB and other secret services justify their existence.
"We needed names to put in our reports. Like collective farm managers we had to report a good harvest. If we had no real agents, we mentioned agents of influence instead," said Lyubimov this week. "Gordievsky is not telling lies. He merely reflects all the ridiculous fuss inside the KGB kitchen and makes it sound very serious. Inside the secret services, and not just the KGB, there is always a lot of fantasy."
The fervour of Gordievsky's campaign to expose the KGB betrays a remarkable faith in the very organisation he defected from. What retired spies like Lyubimov and Kubeykin remember as silly bureaucratic shuffling, Gordievsky sees as proof of the power and efficiency of the secret service. Where others see fantasy, he sees fact.
Instead of claiming credit for a great espionage coup, Kubeykin, the supposed handler of Foot, remembers only dismal failure. He describes his own stint in London from 1971 to 1977 as dominated by frustration and convoluted exercises in self-justification. He says he spent most of his time clipping English newspapers and padding out threadbare reports to Moscow with cocktail conversations.
Hence the obsession with "agents of influence": "Many new terms were invented to show we were doing something. It was all just a camouflage for doing nothing, a bureaucratic game. The more people you mentioned, the more credit you got, the higher your promotion."
The fallout from Sunday's scoop has damaged some of the protagonists more than others. Foot himself appears unscathed. Most people consider the allegations against him to be laughable, but there will be palpable unease among sections of the British Left - not just lunches but junkets to the Soviet Union were common for sympathetic journalists and writers as well as trade unionists and politicians, and many could now be liable to misinterpretation.
As for John Witherow, the publication of the story may make a rapprochement with New Labour more difficult, and there is undoubtedly unease among his staff about the way the paper presented the story. The serialisation of the book begins this weekend, and while Witherow's sales are likely to benefit, the paper's credibility looks to have suffered.
This leaves Gordievsky himself. He supplied the critical intelligence on Mikhail Gorbachev that very quickly persuaded Margaret Thatcher and in turn Ronald Reagan that the former Soviet leader was a man they could do business with. In this respect, he was a genuine "agent of influence", but he may be carving himself a different tombstone: "Agent Grab-it-and- Run".
Additional reporting by Chris Blackhurst.