In Tripoli, after an interview with Colonel Gaddafi, the Libyan leader escorted the British author from his tent. As Yallop's interpreter, Salah, walked ahead, Salah's trousers caught fire from a brazier. Gaddafi nudged Yallop and laughed, shoulders heaving. Yallop called out a warning. But Salah, too embarrassed to beat out the flames, strode on into the night, a beacon of stoicism.
In Algiers he encountered Abu Abbas who, in 1985, hijacked the Italian cruise liner Achille Lauro and threw overboard a crippled Jewish passenger. The author's indignation got the better of his professional curiosity when the terrorist suggested that the passenger might have gone for a swim in his wheelchair.
'I said, you bastard. You son of a bitch.'
'Where are you going?'
'Outside. I don't want to stay in the same room as you.'
Stranger still was a meeting with Abu Nidal in a suburb of Tripoli, the Libyan capital. At 10am, the bald, bloated terrorist was drunk and talkative, acknowledging an Iraqi role in the 1982 attempted murder of Slomo Argov, the Israeli ambassador to London, and suggesting that a Syrian-sponsored attack on an American target was imminent.
Returning to London, Yallop warned MI6 of the threat. 'To my astonishment the MI6 agent was far more interested in Nidal's drinking habits.' Less than two weeks later Pan Am Flight 103 from Frankfurt to New York was blown up over Lockerbie.
Curious as these encounters are, they take a back seat to Yallop's confrontations with his real quarry, Ilich Ramirez Sanchez, or 'Carlos the Jackal'. In his 570-page book, To the Ends of the Earth ( pounds 17.99, to be published by Jonathan Cape on Thursday), an account of the author's odyssey through Europe, the Middle East and the Americas, Yallop meets not one Carlos, but two. The first, interviewed for many hours in Lebanon, turns out to be an impostor, planted to deflect Yallop from the right path. The second, materialising on a park bench in Damascus, satisfies the author that he is the real McCoy.
An exclusive extract from the book appeared in yesterday's Independent. Like his last one, In God's Name, which claims that Pope John Paul I was assassinated, the book will be controversial. Yallop feels he might be in danger, particularly from elements in Syria where he says Carlos is now 'a house-guest/prisoner'. He also feels that the British Government should press President Assad for Carlos's extradition.
The known British crimes of Ilich Ramirez include the attempted murder of Edward Sieff, the Jewish former president of Marks & Spencer, and the bombing of an Israeli bank in the City of London. He is also wanted for terrorist crimes elsewhere in Europe. But, Yallop claims, there has been a Western conspiracy - in which journalists are willing pawns - to make Ramirez the creature of Gaddafi, whereas he was carrying out the dirty work of Iraq (the 1975 attack on Opec's Vienna headquarters), Syria (Lockerbie) and Wadi Haddad of the Popular Front for the Liberation of Palestine (rocket attacks on Orly Airport).
Had not the West demonised Carlos the Jackal, Yallop told me, 'he would have been killed (for messing up a Paris assignment) by Haddad in mid-1975 . . . But Haddad saw the power of the myth that the media created with the help of the intelligence agencies.'
Yallop, 55, is no stranger to controversy. Last year he took the BBC to court over losing his job as scriptwriter on EastEnders. He was awarded pounds 68,000. At the time, he criticised the BBC for allowing the television series to be created by 'middle class people with a middle class view of the working class which is patronising'.
Yallop's own background is working class. His mother, who had been in service in south London, was from Cork (entitling him to an Irish passport, useful for entering Libya) and raised him as a devoutly Roman Catholic schoolboy. His English father was peripatetic. 'He and my mother separated at my birth. He would come back once a year on his visits. Total eccentric. I know he spent a lot of time selling the elixir-of-life at fairgrounds, dressed up as an Indian fakir.' His upbringing, says Yallop, 'gave me an enormous hunger for justice - the desire to pursue truth'.
Between pursuing Carlos and the BBC, Yallop also went after Paramount Pictures, claiming that parts of In God's Name had been plagiarised for The Godfather Part III (the film's publicity material said that story elements were inspired by news reports). Reviews of In God's Name, published in 1984, were mixed: according to the Economist, he presented not a shred of firm evidence for his papal murder allegation, but 'seethes with prejudices, sees every issue and every person in either black or white, and casually blends established fact, hearsay and supposition'.
With his new book, Yallop originally set out to write about the 1982 massacre of Palestinians in the Lebanese refugee camps of Sabra and Chatila. When Robert Fisk, the Independent on Sunday's Middle East correspondent, beat him to it with Pity The Nation he decided to make Carlos his central thread.
Painstakingly, via wide-ranging European and Middle Eastern sources (among them the former Austrian president Bruno Kreisky, and the former Maltese prime minister Mifsud Bonnici) Yallop tracks 'The Most Dangerous Man in the World' to Lebanon's Bekaa Valley, picking up vivid eye-witness material, forming a quite favourable view of Colonel Gaddafi and a quite unfavourable one of Israel's leaders.
The odyssey became worthwhile. Ilich Ramirez Sanchez told Yallop his life story: from birth in Caracas in 1949, via Patrice Lumumba University in Moscow, mistresses in Knightsbridge beds and guns and explosives in Knightsbridge cupboards, to his killing of three French secret police in 1975, and a promise to meet the author for a further talk . . . only for Yallop subsequently to learn he had been listening to an impostor.
But Yallop refused to give up. Nor was he put off by a 'Mossad- inspired' story that Carlos had been murdered and was buried in the Libyan desert. Instead, he combed the West Bank and Gaza Strip for fresh leads, until finally, in Damascus in October 1989, he met the man he believes is Carlos.