George Smiley, John le Carré’s iconic cold war spymaster, is to return for the first time in 25 years in a new novel by the beloved spy-turned-author.

A Legacy of Spies, due to be published on 7 September, will also see the return of Smiley’s colleagues from the British secret service – or the Circus, as they were known in Le Carré’s original books. The bestselling novels famously drew on the author’s own experience of working for British intelligence in the 1950s and 60s.

Though scant details have been released by publisher Viking, a division of Penguin Random House, the new novel will feature Smiley protege Peter Guillam, who in his old age has retired from the world of spooks to a farm in southern Brittany.

Summoned back to London, Guillam and his colleagues are subject to scrutiny for past misdemeanours, committed at a time when there were fewer scruples about the methods used to win the ideological war raging between the west and the Soviets.

According to Le Carré’s agent, Jonny Geller of Curtis Brown, the book was written in “a fever” over the past 12 months. Though Geller refused to reveal details of the plot, he said that it would “close George Smiley’s story”, which began in 1961 with Le Carré’s debut novel, Call for the Dead: “When I received the draft I had to keep starting it again and pinching myself that I was in the company of all these great characters from the Circus,” he said. “It really is going to be one of his finest, if not his finest, novel.”

In its announcement, Viking said A Legacy of Spies would interweave past and present into a single plot as “ingenious and thrilling as the two predecessors on which it looks back: The Spy Who Came in from the Cold and Tinker Tailor Soldier Spy”.

The lugubrious spymaster is most famous for his appearances in the 1970s Karla Trilogy, which includes Tinker Tailor Soldier Spy, The Honourable Schoolboy and Smiley’s People. Those novels concluded with Smiley confronting his nemesis Karla, the Soviet spy chief. Smiley’s last appearance in fiction was in 1990, when he emerged from retirement in The Secret Pilgrim, but he has also appeared on screen in various adaptations, most recently portrayed by actor Gary Oldman in the 2011 film Tinker Tailor Soldier Spy.

It is believed that the author was inspired to revisit his old characters because of the current political situation, although Geller said drawing the conclusion that he will address Moscow’s alleged interference in international elections and alleged ties with Donald Trump’s US administration was “far too simplistic”. “As a readers you can see parallels between what we thought was over and what is happening now,” is all he would reveal.

The news came as it was announced that a nine-year project to move 21 of Le Carré’s novels into Penguin Modern Classics is near completion. The project to convert the titles, starting with his debut and continuing to his war on terror thriller A Most Wanted Man began eight years ago and will be completed by 2018. It will represent the most extensive body of work by a living author to be awarded this status, the publisher said.

In recent years Le Carré, whose real name is David Cornwell, has been critical of Britain’s relationship with the US in the post-Soviet era and of the war on terror. Speaking to the Telegraph in 2008 following the vote to allow suspects to be kept in detention without charge for 42 days, he said: “People call me an angry old man. Screw them. You don’t have to be old to be angry about that. We’ve sacrificed our sovereignty to a so-called ‘special relationship’, which has nothing special about it except to ourselves.”