[5][6][7][8] While in Vienna, he had written his first novel, Down Among the Dead Men, an espionage thriller set in Hong Kong, which was published by Macmillan in New York in 1982 and Hodder & Stoughton in London in 1983.

The decision to leave a salaried job for full-time writing was not easy, particularly with two young children, but Dead Men was widely and well-reviewed on both sides of the Atlantic.

Ted Allbeury welcomed its "rich variety of credible characters, a plot that really hums along and descriptions of far away places that make you reach for the travel brochures.

"[13] Dead Men introduced two characters who would figure in this series of Cold War books – David Nairn, working-class boy from Scotland, who went to Oxford and is now a key player in MI6, and Major-General Nadia Alexandrovna Kirova, who has got to the top of Soviet military intelligence, the GRU, despite being a woman, and is now battling to keep her place in the Politburo.

They continue as antagonists in Hartland's second novel, Seven Steps to Treason, described by The Sunday Times as "A stunning display of diplomatic and undercover knowhow, of SAS dare-devilry and the old global double-cross".

[2] Throughout the 1960s, '70s and '80s, allegations – in newspapers, broadcasting and books – were common currency that the Soviet Union had a "Fifth Man", in addition to Burgess, Maclean, Philby and Blunt, somewhere at the top of MI5 or MI6.

The key to the truth was believed to be Red Army Intelligence Colonel Ursula Kuczynski, who was a Soviet agent undercover near Oxford in World War II.

Finally he ran her to earth (he will not reveal how), living in hidden retirement as a senior party member with the Order of the Red Banner, in East Berlin.

She had spoken to no one from the West for forty years, but made him tea in her kitchen and, a few days later, gave a long filmed interview – the first with a major Soviet spy who had not defected but remained in place and a committed communist.

Her interview provided the core for his 60-minute television documentary Sonia's Report (ITV Channel 3, 1990), detailing her recruitment in Shanghai by Richard Sorge, Stalin's leading agent in the Far East, training in Moscow, hair-raisingly dangerous service with the communist underground in China – and finally to Oxford in 1941, posing as a Jewish refugee from Nazi Germany with two children, but in fact acting as courier for Klaus Fuchs as he betrayed the secrets of the atom bomb to Stalin.

In the War, Fuchs had been allowed a car as a scientist on military work, but "Sonia" had cycled to rural locations near Banbury for their secret meetings – and still had the bicycle in her Berlin cellar.

[2] After Sonia and Gordievsky, he was researching contemporary Islamic politics and terrorism for a second series of espionage thrillers; and published a one-off crime novel Dead Fish under the pen-name Ruth Carrington in 1998.