Philip French was not the first journalist to whom I sent a letter. That accolade goes to John Simpson, who I wrote to when I was 14 and stuck in hospital for the foreseeable future, so nothing seemed more appealing than being a foreign correspondent: all that freedom, flying and distance from the white walls I was then trapped inside. Simpson, to his eternal credit, sent me back a long, handwritten letter, which I still have somewhere, in which he encouraged me to keep writing, find what interests me and never to be afraid to ask those I admire for guidance.

Four years later, I was out of hospital and I was free but now I wanted to spend my days in an enclosed space: the cinema, specifically. My dream had mutated and now I longed to be a film critic. However, this was the mid-90s and my unashamedly mainstream taste didn’t really fit in with most film critics’ perspectives in that indie-driven, Brit-flick-heavy era. To this day I’d rather watch Independence Day a thousand times than Secrets & Lies just the once and, while I never felt the need to apologise for this, it did mean that I struggled back then to think of a critic I should write to for guidance. And then I found Philip.

When people think of Philip’s film writing now, they tend to think of how learned he was. When he died three years ago, he bequeathed his enormous collection of film books and notes to the British Film Institute, and this will be known as the Philip French collection. I say “will be” because the poor folks at the BFI are still working their way through it, trying to catalogue all 3,000 – 3,000! – of his film books, as well as his pages of scribbled notes. Next time you think you have too many books, remember that Philip had so many books just about movies that they are currently taking up 90 metres of storage shelving behind the scenes at the BFI Reuben library.

All that knowledge was in his head; as heavy as those books might now be on the shelves, he wore it so lightly. All that information about westerns and 1960s B-movies and Italian cinema and, well, everything, really, that I still know pretty much nothing about. Here’s a typical Philip line: “I saw only two movies [on holiday in the US]: Woody Allen’s Stardust Memories … and the much-vaunted patriotic nonsense The Great Santini (which I only took in because it was showing at Chicago’s tastefully restored Biograph, the cinema where John Dillinger saw his last picture show on 22 July 1934).” Bear in mind that this came from his review of Caligula, written in 1980 – long before Google made everyone an expert. Facts about 1930s gangsters’ movie habits came as easily to Philip as he then communicated them to the reader, tossed off in casual parentheses.

But when I read his reviews as a teenager I sensed something beyond the expertise, and that was his total lack of film snobbery. Only the insecure are snobs. The truly wise are open-minded enough to see joys in more than their small patch of interests, and I’d noticed this in Philip’s reviews, in which he not only appreciated the kind of movies I liked but also brought in his knowledge of the films he liked, and therefore made me see all movies differently. Take this from his 1990 review of the much-derided Back to the Future III, which he described, pleasingly, as “funny, charming, inventive and affecting”:

“Funny, charming, inventive”: Christopher Lloyd and Michael J Fox in Back to the Future III. Photograph: Allstar/Universal/Sportsphoto Ltd

“Sitting in the local saloon are old-time cowboy actors like Harry Carey Jr, who appeared in Hawks’s Red River and numerous Ford westerns, and whose father was the star of Ford’s first silent pictures…”

He describes how Doc Brown starts to court the schoolmarm in the scene “by carefully imitating the way Henry Fonda’s Wyatt Earp escorts Cathy Downs on to the dancefloor in My Darling Clementine. Marty survives a gunfight by remembering Clint Eastwood’s cunning strategies in A Fistful of Dollars. The supporting characters behave according to a traditional European view of society, which believes that your ancestors and your progeny are likely to be much like you. … But though young Marty’s jeans determined his name when he was inreturned to 1955 (he was dubbed Calvin Klein), his fate is not determined by his genes. He has that American belief in the ability to challenge fate and re-shape one’s life by an act of will.”

Or this, on Home Alone, also 1990:

“Just as Straw Dogs reflected anxieties bred by Vietnam, [Chris] Columbus’s picture preys on frustrations created by the Gulf confrontation. It feeds off a desire to solve problems rapidly through heroic combat so that the family can return home to Middle America from threatening foreign parts and hug each other around the tree on Christmas morning.”

I’d never read anything like this. Philip thought about films – my kind of films – as much as I did, but far more knowledgably and thoughtfully. So, obeying John Simpson’s dictum, I wrote to him at the Observer. Could he please tell me how I might become a film writer one day? Philip wrote back right away: of course, he said – but perhaps it would be more enjoyable if we had this conversation in person. Could I meet him for lunch in Soho next week? And perhaps accompany him to some film screenings? I was 18 years old and it was the summer between finishing A-levels and going to university. I’d never had less to do in my entire life. I wrote back and told him I reckoned I could manage that.

Do adults know how much they can influence the lives of teenagers? It’s easy to forget this: teenagers can be so surly and uncommunicative, adults are so busy – really, why bother? I know I fall into that trap sometimes: surely this 17-year-old doesn’t really expect me to write back, I’ll think fretfully at 3pm on a Monday. And then I remember how much John Simpson’s and then Philip’s letters changed my life, and I write back.

Macaulay Culkin in Home Alone. Photograph: Alamy

I met him in Soho in front of a mysterious dark building, which turned out to be, as he explained to me, a screening room. He was so polite and self-effacing that it was hard to be starstruck but I was, utterly. I felt like such a fraud next to him – what did I know next to this titan of film criticism? Literally nothing. We both must have known this but, as he took me into the screening room – to see the Merchant Ivory film Feast of July – he asked what film directors I liked (Tim Burton, Robert Zemeckis), what film magazines I liked (Empire, obviously) and what I was going to study at university (English literature). I was so dazzled at getting to see a movie in the middle of the day – and for free! - I didn’t realise how extraordinary it was that this man was being so generous with me while he tried to do his job.

Afterwards, he took me for lunch at an old-fashioned Italian restaurant and asked me what I thought of the movie and how I would write about it. I talked about me for an hour, forgetting that the whole reason I was there was to talk about him. We then went back to the screening room and saw – if memory serves – Kingpin. When that finished, he told me to stay in touch. I thanked him and trotted off, ruined for ever, because I would thereafter take it for granted every working day should be as fun as the day I’d just had, watching movies and eating spaghetti with Philip. He made journalism seem like a perfectly realistic ambition for me, which is odd because he was so much more learned than I was and am. But his kindness gave me delusions beyond my abilities, and they propelled me forward.

I did stay in touch, and when I wrote to him at the end of my second year and said I was now interested in writing about fashion he arranged for me to have work experience on the Observer’s fashion desk. When I graduated from university and got a job on the Guardian’s fashion desk I worried that he’d feel like he’d wasted his time on me now that I wasn’t going to be the next Pauline Kael. I’d turned out to be a fraud after all, I thought guiltily. But after he died I learned that he’d saved my letters to him from two decades ago, and then I cried.

On Tuesday, I’ll be giving the third annual Philip French memorial lecture at the Bristol Festival of Ideas, in the city where Philip himself first started working as a journalist. I no longer feel like a fraud in my job, but I feel like a bit of one giving this lecture. Clearly he deserves more than me. But I also like to think that he wouldn’t have minded too much. He was too kind to think like that, too devoid of intellectual snobbery. And he probably would have taken me out for spaghetti afterwards.

Hadley Freeman gives the 2018 Philip French Memorial Lecture at the Bristol Festival of Ideas on 16 October. The Philip French Collection will be available online and free to view in the BFI Reuben Library from 2019. Notes from the Dream House: Selected Film Reviews 1963-2013 by Philip French is published 25 October (Carcanet Press)