What is the biggest threat to reading in today’s culture? Price-cutting Amazon, or ghost-written celebrities? Library closures, or dwindling literacy?

None of these, according to literary super-agent Jonny Geller. The answer is Netflix.

“It’s addictive,” he says, “and it’s good.” People are now as likely to gobble up box sets as thrillers. And so authors (like me) and agents (like him) must adapt to survive. He, at least, seems to be doing that rather successfully.

In the last year, Curtis Brown, the agency where he is joint CEO, has taken over three other businesses including the agency owned by the late Ed Victor, who personified the old-style, convivial publishing world of book deals struck over long lunches.

“Ed had a great life with his authors,” he says, “but there wasn’t a large amount of planning.” Curtis Brown, he adds, does things differently. “We’re building a business.”

That business isn’t scared of Netflix and co, because a decade ago they realised they were perfectly placed to create content for the large and small screen. The latest example is McMafia, coming to BBC1 on New Year’s Day, part-produced by Cuba Pictures, Curtis Brown’s film-making arm and based on a non-fiction book by one of the agency’s authors, Misha Glenny. Starring James Norton, it’s a drama based in the world of international organised crime, with a cast list including at least one shady Israeli businessman, filmed in 11 locations, including Belgrade, Belize, Qatar and Tel Aviv.

Curtis Brown represents screen writers, directors and actors as well as authors, so they knew the journey from selling screen options to finished product was slow and often unsuccessful. “It made sense to speed up the process,” says Geller, “and put money into developing projects of our own.” Their first film was Boy A, starring Andrew Garfield, and they were also behind the TV adaptation of Susanna Clarke’s Jonathan Strange and Mr Norrell.

Curtis Brown has come a long way since it was set up in 1899. Geller says that even in the 1990s when he joined, it was still trading very much on its past, looking after the estates of luminaries such as Winston Churchill and John Steinbeck. But in 2001 there was a management buyout by Geller and four colleagues, and the company started looking to the future.

British writers deserve to be celebrated, he believes, and he is baffled by government policies that don’t seem to understand that.

“I go and speak at schools and I tell the pupils that the creative industries bring in £92 billion to this country. And yet in so many schools they are cutting music and drama and art from the curriculum, and pushing tech and science.”

He’s on a mission to “demystify” publishing, and break down old perceptions that it is snobbish. Although he grew up in a comfortable, middle-class home in Cockfosters, north London, and went to a private school, City of London Boys, he still had a perception of the industry before he joined it as being “very closed — very English people having dinners in Tuscany together. I thought I’d never be part of that world.”

The need for more diversity is a current talking-point in the industry, and Geller says it is important not to just be “glib and liberal” about it, but find a way of attracting “new people and voices who represent our society and not just a section of it.”

It’s difficult to make the industry more diverse though, he says, because starting salaries of £20,000 effectively rule out those who can’t afford to live in the capital. He talks about bursaries and sponsorships… the need for government support, but seems startled when I suggest that Curtis Brown could move some of its operations out of London, seeking new talent and training new agents in Manchester or Newcastle. It would save money, he agrees. It might also provide more access to the agency’s creative writing courses (the first offered by an agency in the UK), which start at £200 for an online option, but build up to an eye-watering £2,990 for a six-month novel-writing course.

Geller’s ambition for his writers is clearly that they will do considerably better than £11,000 a year, which is the sort of annual income earned by most British writers.

The gap between bestsellers and the rest is “more and more stark” he says, and even a Man Booker Prize is no guarantee of good sales any more. He says it’s impossible to predict which books will take off, but they are the ones which leave you “remembering the feeling of reading the book… you might not remember the plot or the characters, but you remember how much you loved the book, how moved you were by the characters.”

Selling, he says, is a matter of planting ideas in an editor’s mind, so they think that they have done that work themselves, that the clever strap-line on a book’s cover is their idea, not his. But does a writer need to have that strap-line in mind before they start writing? (I ask, because I never do this). It depends, he says, thinking of some of his illustrious clients. William Boyd knows exactly what he’s doing before he starts writing. Howard Jacobson has a basic idea, but never plans ahead (like me). John Le Carre has a long thinking time, and then quite a quick writing time. “To sell a book, you do need to know what it’s about, and to be able to put that into ten words or so.”

Agenting wasn’t Geller’s first career, and books weren’t his first love. But he was a member of Habonim, the left-leaning Zionist youth movement that acted as a creative cradle for so many young Jews in the 1980s, and, after A levels, went on its gap-year scheme to Israel. There, he “ate up the kibbutz library”, falling in love with writers such as Milan Kundera and Gabriel Garcia Marquez, authors who “took me into the world”. A degree in English and European Literature at Warwick University followed, but he spent most of his time there acting —“I think I was in 30 plays in three years” — heading for drama school after he graduated.

A career as an actor followed, with a sideline in door-to-door selling to pay the bills. But, at 35, he had “a mid-life crisis,” looked at the success of some of his contemporaries and realised he would be “angry and sad” unless he changed track.

He thought he could combine his love of books with his skill for selling, and found a job at Curtis Brown, assisting the woman who administered the estates of A A Milne and C S Lewis. After two years of “hard graft” on Winnie the Pooh’s behalf, his boss left and Geller was effectively without a job. Hoping no one would notice, he “hid” in the office, one day reading a manuscript plucked from the slush pile of unsolicited novels that every agency is sent. He thought the story, about a man taking revenge on his teachers, was great; told the author that he was an agent, and then sent it out to four editors, pretending the same thing. He spent the weekend convinced he would be sacked for deceit, but returned to the office to find that all four wanted to bid for the novel. The eventual deal won the author a stupendous (for the mid 1990s and for today) £500,000 advance, and Geller cemented his rise to agent status by making sure the story appeared in the Guardian. There’s a sting in the tale though, the revenge book came out on the day of the Dunblane massacre, and, doubtless as a result, didn’t sell.

He has written one book himself, and it could not have been more Jewish — or less Anglo-Jewish. Yes, But is It Good for the Jews? examines everything from Agatha Christie to Volkswagen, asking that question usually heard from elderly relatives when watching TV.

Just the idea made me cringe, I tell him, which delights him. It was never meant for the British market, he says, he got the idea on a flight to America and submitted it to publishers there under a pseudonym. A British deal came later.

It was fun, he adds, and he’s glad to have had the experience of writing a book, spending time alone with his computer —“the only time in my week that no one interrupted me” — feeling completely engaged with just one project. One book was enough though, and he feels you should only write books “because you can’t not,” the same going for acting, the career he abandoned.

“Being Jewish is very important to me,” he says, although he says it’s by accident rather than design that his client list includes so many Jewish authors, Jacobson of course, and Linda Grant, Tracy Chevalier, Robert Peston, Rabbi Jonathan Wittenberg…plus non-Jews who have a great interest in Jewish affairs, such as former prime minister Gordon Brown and Tony Parsons.

He and his wife, Karen Mattison (who runs Timewise, a recruitment agency for part-timers, and advises him on flexible working for his predominantly female workforce) are members of Muswell Hill Synagogue, and have brought up their three sons, aged 11, 16 and 19 in a traditional Jewish home. Has he produced three readers? His 19-year-old is studying Politics at York and his father doesn’t think he reads much.

His youngest does read, and the middle one? “He’s a big consumer of box sets. But that’s fine — if they are good.”