"There was a time," Len Deighton reflects, rather savouring the memory - "it's difficult to believe now - but before the film came out, Michael was still a struggling actor and I was a famous writer. Of course, he overtook me like a skyrocket, but there was a brief period of time when I was more famous than Michael."
The Michael to whom he refers is Michael Caine. And the Caine connection - it even sounds like a discarded title for one of Deighton's pacy, hard-boiled spy thrillers, which exploded on to the book stalls in their distinctive white covers in the early 1960s - was, as you have probably surmised by now, The Ipcress File, Deighton's first novel.
It was not Caine's first leading film role; that distinction is reserved for Zulu. But it was before Alfie, and Caine acknowledges that the chippy, working-class spy with an attitude problem was a much better showcase for him than the patrician Lieutenant Bromhead at Rorke's Drift. He even remembers reading bits out of the book to his then flatmate Terence Stamp, saying, "Listen to this, Terry, I could do this", and Stamp retorting that, first, they would never make a film of it and, second, even if they did, Caine would never get the part.
Harry Palmer became a defining role for Caine, with two further outings in Funeral in Berlin and Billion Dollar Brain, all based on Deighton novels (in which, famously, the character had no name). At a time when working-class heroes were suddenly in vogue, here was a man who lived in a bedsit, went to work on the bus, was paid a weekly wage and, if he needed a gun, had to get a form countersigned by his boss.
All three films are to be shown in a retrospective of Caine's career at the National Film Theatre this month, including a new print of Sidney Furie's The Ipcress File, which gets an extended run and a limited national release. Deighton will be appearing, too, in the British media for the first time in more than 20 years. An hour-long documentary about him (which includes an interview with Caine) is also due to be broadcast on BBC4 this month, along with two of the films. In a wide-ranging discussion, Deighton acknowledges that if the films were good for Caine's career, they didn't do his any harm, either.
Aged 33 when the book came out, and with his bookish manner and heavy spectacles - like the ones Harry Palmer wears - Deighton may not have seemed an obvious candidate to become one of the hottest names of the 1960s. In some ways he looks rather more spry and dapper now, at 76. He has certainly lost none of his restless, inquiring energy. But, as Sir Max Hastings observes in the BBC4 film, "To those of us who were in our twenties in the 1960s, his books seemed the coolest, funkiest, most sophisticated things we'd ever read." Their sharp-tongued lack of respect for authority and old-fashioned bureaucracy caught the mood.
Nor was it just the spy stories. Already a successful illustrator before he turned to writing (among his more improbable credits is the first British cover for Kerouac's On the Road), Deighton seemed to know no limits. An excellent cook (he had learnt in the kitchens of the newly opened Royal Festival Hall, where he worked during vacations from art school in the early 1950s), he became The Observer's cookery writer; copies of his illustrated cookbooks now change hands on eBay for substantial sums. He wrote guidebooks, was photographed with Patti Boyd and Twiggy, acquired the ultimate jet-set sinecure as travel editor of Playboy, and then became a film producer himself.
Even so, he was a bit taken aback when the phone rang one day and it was Bertrand Russell. "I knew he was a famous philosopher but I didn't know he had my phone number," he says. It turned out Russell wanted advice on the management of his literary estate rather than on the meaning of life. But at the end of their meeting, he mentioned that Paul McCartney wanted to meet Deighton the film producer. Having produced a film, starring David Hemmings, of his own novel Only When I Larf, Deighton and the photographer Brian Duffy had bought the rights to Joan Littlewood's Oh! What a Lovely War. McCartney and the rest of the Fab Four were interested in making an anti-war film themselves. And so it was that McCartney came round for a curry in Deighton's Elephant and Castle flat in 1967. It was that sort of time.
Oh! What a Lovely War was duly released in 1969, though without The Beatles, who wanted to use modern music rather than the music-hall songs of the original. One of the issues that Deighton attempts to settle in the BBC4 film is why he took his name off the credits as producer, something he now describes as "stupid and infantile". It was not that he was dissatisfied with the film. It was the endless stream of people demanding credit for work that, as far he was concerned, they hadn't done. "I thought these people should be ashamed of claiming things they hadn't done. So I thought I would shame them by taking my name off. It doesn't matter. The film got made. In a few years it will be turned into banjo picks."
It was the last time Deighton would mess with the movies. "I realised after having that multimillion-dollar Hollywood singing-and-dancing film on my hands that solitary life behind a typewriter wasn't quite as bad as I had been thinking," he says now.
So he returned to writing, notably several important books about the Second World War, through which he had lived as a child. Bomber was a thinly fictionalised account of an area bombing raid over Germany in 1943, seen - and this, along with the devastating accretion of telling detail, was what shocked people - from both sides. Fighter was a formal account of the Battle of Britain, but one that again provoked outrage, including the German point of view. The research was so meticulous that his conclusions, chiefly that the Few were very brave but their leaders were daft, could not easily be set aside. Indeed, they are now part of the orthodoxy.
Superficially, these books have little in common with the spy stories or Deighton's other novels. If there is a common factor, it is his sympathy with what you might call the poor bloody infantry. Even now, he will not concede that he has any agenda against the generals, the leaders, the politicians, even after his most recent book, Blood, Tears and Folly, a damning overview of the major campaigns of the Second World War.
What he does say is that people in positions of power, who may be sending people off to be killed, should expect to have their deeds examined in rather more detail than those being sent to be killed. It is tempting to see it as a straight class issue. But he deflects the question.
"I was born in a workhouse," he says. (He was, in Marylebone in London, in 1929, though it was just up the road from the hospital, and his parents were by no means destitute; at that time, his father was a chauffeur and skilled mechanic, "in service" to the family of a senior keeper at the British Museum. His mother was a cook. They all, in fact, lived in a mews near Baker Street.) "It trumps the ace of everybody else, doesn't it? Where do you go that's lower than that? So I feel free to criticise anyone I choose. I just speak as I find. I'm not a member of any political party. I hesitate before I join hands, as the old saying goes. What I say is based on my own experience."
'The Truth about Len Deighton', produced and directed by Robert Dawson Scott, BBC4, Saturday, 9.15pm. The NFT Michael Caine retrospective runs to 26 January ( www.nft.org.uk)