Trying to find John le Carré's rambling cliff top home in deepest Cornwall is rather like trying to solve the plot of one of his spy thriller novels – difficult.

It's not just the twists and turns and the dead-ends, or the unhelpful signs which give no clue at all as to whether you're actually travelling in the right direction, it's also the fact that the house is only discovered after negotiating a long distance of uncomfortably rough terrain.

But when you eventually find it, overlooking miles of sparkling deep blue sea, it is easy to see why the three old derelict stone cottages and barn that he and his wife Jane have painstakingly turned into one beautiful structure have become the refuge of one of our country's most famous spy novelists.

"I love it here, particularly out of season," he says, as he gazes out across the bay. "The empty landscape, walking on the cliff, and the light, which of course everyone always mentions ... but it seems that I can think well here. I can populate the empty landscape with my imagination."

It is a lucrative imagination. The author of Smiley's People, Tinker Tailor Soldier Spy, The Constant Gardener and the definitive The Spy Who Came In From The Cold – all best-sellers which have been made into acclaimed films or television series – is undoubtedly a millionaire several times over.

At 78, he could easily retire to an exotic island like that other master of the spy genre, Ian Fleming, creator of James Bond (once dismissed by le Carré as simply being a "gun for hire" rather than any kind of serious political agent), who lived in some splendour on an estate in Jamaica.

But David John Moore Cornwell, the man behind the le Carré nom de plume, prefers the peace and solitude, the low-key friendships and community, that he has found on a cliff top near Penzance.

"The Cornish leave people alone, which is wonderful," he explains. "Here, I don't see many people. I write and walk and swim and drink. Jane and I have put our hearts and souls into this place. We love it here."

A grandfather 12 times over (from his three sons by his first wife, Ann, who died last year) and about to become one again (by his fourth son Nicholas – who writes as Nick Harkaway – the only child from his long and happy marriage to Jane, whom he married in 1972) David Cornwell could be forgiven for putting his feet up, taking it easy and simply enjoying the heavenly views.

But now his 22nd novel, Our Kind of Traitor, is about to be published; a new film (of Tinker Tailor Soldier Spy, which starred Alec Guinness in the original BBC series in 1979) is about to go into production – with stars including Gary Oldham as George Smiley, Colin Firth and Benedict Cumberbatch; plus, he has already started his 23rd novel.

He laboriously writes out all his manuscripts by hand, and Jane, a former book editor, types it up for him. He works in the old converted barn which he bought all those years ago, after he fled to Cornwall after he break-up of his first marriage.

"When my first marriage, broke up, like any decent person in that situation, I was desperate and in total despair," he recalls. "I felt the lure of the peninsula, and came to stay with my friend John Miller, the painter. John lived with his partner, Mike, in a house at Sancreed, and I took the top floor. They kind of adopted me. I started walking here, and really fell in love with the place."

While out walking with John the pair noticed the derelict cottages. "The farmer was actually out in the field, and I spoke with him and practically bought them over the plough.

"I bought the whole lot, including nearly a mile of cliff, for £9,000 – enough then to buy a London house – but we've since given the land to the National Trust."

Despite the peace and tranquillity, the world of espionage is never far from his mind. It is a world he once knew very well. He too was once a "spook", a former secret agent working for both MI5 and MI6 during the Cold War – during which time secret assassinations were carried out by British intelligence.

Born in Poole, Dorset, in October 1931, he went to boarding school at the age of five, after his mother Olive left his father, Ronnie – a confidence trickster and insurance scam fraudster who spent several years in jail – leaving David and his elder brother Tony to cope alone at what he calls "English public school gulags".

Ronnie, apparently, was into all sorts of murky dealings. Although he himself was from a very strict, working class, non-conformist family, and his three sisters all married lay preachers, he turned to a life of crime, and became friends with the likes of the Kray brothers (Cornwell knows this, because his half-sister, the actress Charlotte Cornwell, once found a picture of their father with the Kray twins while researching a film role).

But, as the author well knows … "the membrane between criminal activity and orthodox activity is extremely thin", and success from one lifestyle can reap rewards in another… until, that is, you get caught. It is, of course, the abiding thread running through each and every one of his books, as each of his protagonists tries to uncover layer upon layer of yet more secrets and lies.

"My father was quite brilliant," he reflects, sipping a cup of hot coffee while sitting in a deep, comfortable sofa in his elegant wood-panelled living room.

"If he'd only been straight, he'd be a billionaire. He reinvented himself, again and again ... multiple lives, multiple loves, different identities for different people. But for the children, we came from a background of strong regional accents and very simple working class tastes... my father's greatest ambition was to turn us into gentlemen and send us to smart schools. He had the money."

Young David was sent away to Sherborne School, Dorset, where the "anti-culture" of bullying so disgusted him that he left at 16.

He didn't actually see his mother from the age of five until he was 21, when he tracked her down to Suffolk. Like a scene from one of his novels, they met at Ipswich railway station… and stayed in touch until she died. "She was broke, and later, when I made money, I helped to resettle her, and I kept her in later life," he says.

All that feeling of childhood anger and disenchantment would later be channelled into the novels. But to this day, hardly surprisingly, David Cornwell finds it "very difficult to have normal filial feelings towards either of my parents". In his novel A Perfect Spy Ronnie becomes Rick Pym, scheming con-man father of protagonist Magnus Pym. It was good therapy for his son.

Fantasy, he insists, is what his books are all about. He once said: "Nothing I write is authentic. It is the stuff of dreams, not reality. I do not write espionage handbooks… but I am flattered that my fabulations are taken so seriously."

This may be, but his books are undeniably authentic, informed as they are from his time working for the intelligence services. After Sherborne, he took himself off to Switzerland, where he studied German literature. It was later, at Lincoln College Oxford, where he got a first in modern languages, that he would be recruited into the ranks of MI5.

He taught at Eton, from 1956 to 1958, before joining the British Foreign Service from 1959 to 1964, serving in the British Embassy in Bonn, then as political consul in Hamburg – good cover for a special intelligence officer tapping phone lines and effecting break-ins. He started writing his novels while still a "spook", in 1961, changing his name to John le Carré, because Foreign Office rules prohibited publish under his own name.

During his time in intelligence, he felt he was operating with just cause. "We did see ourselves as people dedicated to finding out the truth, no matter how painful," he says. "We believed in justice. The sadness to me of the recent Iraq 'dodgy dossier' and the involvement of John Scarlett (the former head of MI6), was that it seemed to me this was no longer happening... the objectivity and the detachment we swore by from Government pressure had been eroded."

Today he watches in varying degrees of amazement and amusement as the plots of his fast-paced spy thrillers, with their political intrigue and complex denouements, appear to leap into life every time he opens a newspaper, or switches on the TV.

Take, for instance, his latest novel, Our Kind of Traitor. It revolves around a Russian money-launderer, Dima, who has been responsible for turning billions of dollars worth of "black" money – from drugs, gambling, extortion and the like – into "white" or clean money, on behalf of the Russian mafia. Sensing his time of usefulness to his Russian "vory" brotherhood is coming to an end, Dima seeks asylum in the West.

No sooner had the book been written, than there's a news story in The Observer, in December 2009, in which Antonio Maria Costa, head of the United Nations Office on Drugs and Crime, said $325 billion in criminal proceeds had effectively been laundered by financial institutions and used to keep the West's financial system afloat at the height of the global banking crisis. The money was the only liquid capital available to some banks on the brink of collapse.

There had, of course, a year earlier, been the rather amusing story dubbed "Yachtgate", when the then Trade Secretary Lord Mandelson, Shadow Chancellor George Osborne and Russian multi-billionaire Oleg Deripaska – a close friend of banker Nat Rothschild – had all been pictured having drinks together on a yacht in Corfu. In the new novel, there is a party scene on a yacht involving similar-sounding types.

"The use the intelligence community makes of commerce, industry, private business and so on, is, I think, becoming quite corrosive," he says.

"Apparently, in the USA there are just under one million human beings cleared for top secret; I wonder what the equivalent is here now, in Britain? I find this cult of secrecy that has grown up deeply disturbing."

He deplores the use of the catch-all phrase "terrorism", which he feels is just an excuse for the continual erosion of civil liberties. "The Counter Terrorism Act corrupted the police service to a great extent, and gave them powers they shouldn't have. These erosions of our civil liberties were one of the most disgraceful aspects of the Brown/Blair government – but they are now being corrected, to a point."

What with the body of an MI6 worker found padlocked inside a sports bag in his London flat ("My strong suspicion is it's entirely to do with his personal life... but it of course raises questions about the selection process") and spy swaps in Vienna, you simply couldn't make it up.

Unless, of course, John le Carré already has …