After a dozen novels and 70 million book sales under his belt, British writer Frederick Forsyth told AFP he is giving up on thrillers because his wife told him he can no longer travel to adventurous places.

"I'm tired of it and I can't just sit at home and do a nice little romance from my study," said the 78-year-old, who revealed in a memoir last year that he had worked extensively for the MI6 spy service.

"I ran out of things to say," said the soft-spoken Forsyth, who trained as a Royal Air Force pilot before joining Reuters news agency in 1961 and beginning his career as a novelist in the 1970s.

After his last trip to Somalia as research for "The Kill List", Forsyth said 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, said 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 said.

He said his memoir "The Outsider" was his "swan song".

"How many bakers go on baking after 78?" he quipped.

In an interview on the sidelines of a speaking engagement organised by the London Grill Club, Forsyth also spoke about his work for MI6 in Africa and the former Soviet bloc during the Cold War.

The writer said 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 said 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!" said Forsyth, dressed in a light-coloured suit.

Secret missions

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 called "Ronnie" who wanted "an asset deep inside the Biafran enclave" where there was a civil war between 1967 and 1970.

Then, in 1973, Forsyth said 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 said 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 said decades had passed and many secrets from that time had already been divulged.

'Insulting' Brexit campaign

His first novel 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 the Daily Express in which he often writes about counter-terrorism issues, military affairs and foreign policy.

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

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

Following his retirement from fiction, he said 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.