After his last trip to Somalia as research for The Kill List, Forsyth says his wife told him: “You’re far too old, these places are bloody dangerous and you don’t run as avidly, as nimbly as you used to.”

Forsyth, who has only ever written on a typewriter, says he had tried an online search for Somalia but had been “very dissatisfied” with the results. “There was some statistical information on Somalia but not what I wanted, which was atmosphere,” he says. His memoir The Outsider is his “swan song”, he says.

“How many bakers go on baking after 78?” he quips.

Forsyth also spoke about his work for MI6 in Africa and the former Soviet bloc during the cold war.

The writer says he would submit draft pages from his novels to MI6 to check that he was not divulging sensitive details and they would sometimes come back with annotations and paragraphs underlined.

In The Fourth Protocol, he says he avoided telling readers how exactly to trigger a nuclear weapon, after a bit of editing of the draft from MI6. “You don’t want anyone actually to do it!” says Forsyth.

Forsyth worked for Reuters and the BBC in the 1960s in France, Nigeria and East Germany.

While working as a journalist in 1968 in Nigeria, he was approached by an MI6 man named “Ronnie” who wanted “an asset deep inside the Biafran enclave” where there was a civil war between 1967 and 1970.

Then, in 1973, Forsyth says he was asked to conduct a mission for MI6 in communist East Germany. “There was an asset, a Russian colonel, working for us deep inside East Germany and he had a package that we needed brought out,” he wrote in his memoir.

Forsyth said he drove his Triumph convertible to Dresden and received the package from the Russian colonel in the toilets of the Albertinum museum. He calls the secret services “our protectors” and says he was not paid for his work, adding: “I was only trying to help out the old country.”

Talking about his work with MI6 could be formally a breach of the lifelong commitment to discretion undertaken when he signed the Official Secrets Act, but Forsyth says decades have passed and many secrets from that time had already been divulged.

His first novel, published in 1971, The Day of the Jackal, was about a fictional assassination attempt on French president Charles de Gaulle by right-wing extremists angry at his granting independence to Algeria. It was turned into a classic film starring Edward Fox.

Other bestsellers quickly followed, including The Odessa File (1972) and The Dogs of War (1974).

After the end of the cold war, he wrote thrillers about al-Qaeda, drone warfare and rendition.

Forsyth also has a weekly column in British tabloid newspaper the Daily Express, in which he often writes about counterterrorism issues, military affairs and foreign policy.

As a longtime advocate of Brexit, Forsyth said he was pleased with the result of the referendum on British membership of the European Union in June but found the campaign was “vituperative” and “unnecessarily insulting”.

He says political correctness has become “a new religion” in Britain and is deeply critical of a justice system he sees as skewed towards the rich.

After his retirement from fiction, he says he will focus now on a campaign for Alexander Blackman, a Royal Marine sentenced to life imprisonment for shooting an injured Afghan fighter in 2011.