A posthumous novel by John le Carré will be published in October to coincide with what would have been the master spy writer's 90th birthday, his agent said on Thursday.

Jonny Geller said Silverview, which was penned before the author's death from pneumonia in December aged 89, will give fans a final chance to hear his distinctive voice. 

Silverview is centred around an "unlikely friendship in a seaside town" between a former city banker and a Polish émigré, he told BBC radio. 

"What you discover, as with all le Carrés, as it comes layer upon layer, is that there's actually the intelligence services get involved because there's been a leak."

Le Carré – real name David Cornwell – left an indelible mark on English literature and recreated the British spy novel in his own image, mixing tales of international espionage with gritty realism.

The breakthrough novel by the former intelligence officer turned writer, The Spy Who Came in From the Cold, and his seminal Tinker Tailor Soldier Spy, dealt with the world of Cold War spies but his later works moved with the times.

His books have been adapted numerous for both film and television over the years.

Publishers Penguin Viking have said in Silverview, le Carré turns his attention to "the world that occupied his writing for the past sixty years – the secret world itself".

Le Carré wrote many novels, some of which have been adapted to the silver screen. Photo: Twitter.com

The novel is a "mesmerising story of an encounter between innocence and experience and between public duty and private morals", it added.

Geller said his first reading the completed manuscript for the book had been a "bittersweet" moment of "mixed emotions" as he could not phone le Carré to give feedback.

"You're immediately back in his company... on the page, he's such a distinctive voice. And the story was so polished and beautifully done," he added.

The agent told The Guardian newspaper le Carré had given his sons "his blessing" to publish the book and they are currently cataloguing his archive of unpublished work.

When pushed on whether further posthumous works might be in the pipeline, however, Geller responded that he had "no comment".

Silverview will be published on October 14. Le Carré would have turned 90 on October 19.