Few film critics can boast that they were employed to pick winners at the races before doing likewise for movies, but Derek Malcolm, who has died aged 91, was the Guardian’s racing correspondent before he became its longest-serving film critic, between 1971 and 1997, following this with a stint at the London Evening Standard from 2003 until 2015.

He put his experience as a critic to good use when he became director of the British Film Institute’s London film festival for three decisive years in the mid-1980s, making this a livelier, more inclusive event, helped by such novelties as a surprise film, and screenings outside London.

Derek defined himself as a reviewer rather than a critic, having started at a time when more judgmental figures were leaving the arena. Among many choice anecdotes, he recalled that one of his predecessors on the Guardian, Richard Roud, was fired for dismissing The Sound of Music in a one-word review: “No”.

But if Derek was more inclined to balance negative with positive assessment – his even-handedness would irk some cinephiles – he also had notable enthusiasms. One of these was Indian cinema, especially the movement known as Parallel cinema in the 70s and 80s, headed by such directors as Shyam Benegal, Mrinal Sen, Adoor Gopalakrishnan, Ketan Mehta and Mani Kaul.

Serving on the Fipresci jury at Cannes in 2007, when the main prize was awarded to the austere Romanian film 4 Months, 3 Weeks and 2 Days, Derek lamented the absence of any films from India. Typically broadminded, he had co-authored Bollywood, a book on popular Indian cinema, in 2002, but was thwarted in plans for a major Indian retrospective at the BFI by the lack of available prints from an industry with a notoriously scant regard for its history.

The decades of Derek’s tenure at the Guardian saw major shifts in the film business, of which the most important was probably the arrival of home video in the early 80s. In Britain, this was accompanied by an outbreak of moral outrage, largely directed against low-budget horror films with provocative titles, collectively dubbed “video nasties”.

As the idea that these could irrevocably damage children gained traction, especially among Conservative MPs and campaigners such as Mary Whitehouse, Derek found himself testifying in court on behalf of the movie titled Nightmares in a Damaged Brain.

When he described it as “not a classic, but well-executed”, he could scarcely believe the judge’s response: “So was the German invasion of Poland.” Such was the hysteria that accompanied the arrival of video, which would lead to a tightening of Britain’s draconian film censorship. But Derek had many opportunities to defend challenging films of vastly greater integrity, including Ken Russell’s The Devils during its protracted struggle to be seen as originally intended.

Derek’s own early life was not untouched by violence and controversy, albeit of a distinctly English variety, as revealed in his 2003 memoir Family Secrets. He was born in London, the only child of elderly parents, Dorothy (nee Taylor) and Douglas Malcolm. His father belonged to a wealthy Scottish family and had been an officer with the Royal Artillery. Fifteen years before the arrival of young Derek, Lieutenant Malcolm had shot his wife’s lover, before becoming the first man in British legal history to be acquitted on grounds of justifiable homicide. Despite the inevitable scandal, Dorothy and Douglas remained married, although living eccentric and largely separate impoverished lives in Bexhill, East Sussex.

Derek discovered the scandal as a schoolboy, when he found a book about famous legal cases in his father’s study with a chapter ripped out. Deeply embarrassed, his father felt he had to confess. “He told me he had something to tell me, and he dreaded it. I just said I knew, quite understood, would have done the same myself.” Derek had obeyed his father’s request and not mentioned it to his mother, so regretted never hearing her side of the affair.

When young, his mother had been a fine singer and occasional performer, who had impressed Arturo Toscanini, and she continued to have many admirers, one of whom would later help Derek enter Merton College, Oxford, where he studied history.

Before that, he had attended Eton, where the scandal was never mentioned. Writing his memoir, reluctantly, at the prompting of his second wife, the journalist and historian Sarah Gristwood, whom he married in 1994, was an attempt to overcome the lurid prejudice of the original reporting, “portraying my mother as an idiot, with this dastardly Jewish brute [her lover] pursuing her, whereas my father was a hero, a gentleman, for protecting her honour.”

The memoir records Douglas’s kindness, even though Derek had learned shortly after his death that the Italian ambassador to Britain was his biological father. There were also happier memories, one perhaps foreshadowing the route that led to film criticism. In 1947, Dorothy took her teenage son to see Laurel and Hardy performing on stage at the London Coliseum.

Derek’s account of meeting them after the show reveals a shrewd economy and sensitivity, especially describing their business with a bun. “Hardy took a bun from the tray, placed it on his chair and sat on it. It was, of course, squashed flat. I’m pretty sure he did it to amuse me. But you never knew with Hardy, who preferred playing golf to working. Laurel looked horrified, especially when Hardy offered the flat bun to me. He was the master of most situations and the pair’s directors invariably deferred to him on set.”

Among other roles before journalism, Derek was an amateur national hunt jockey and spent three years acting in provincial rep. He arrived at the Guardian in 1962, via the Daily Sketch and the Gloucestershire Echo, and recalled that “moving from subediting to horse racing and then to the cinema may seem an odd progress. But in those days it was not so peculiar. The Guardian had a tradition of its writers being all-rounders.”

Despite being at the centre of Britain’s film culture for 50 years, and playing important roles in international critics’ associations, Derek remained exceptionally approachable, modest and enthusiastic. At a birthday gathering last year, he plied me with recommendations of new films to see (as well as avoid).

Speaking recently to his successor, the Guardian’s Peter Bradshaw, he explained that he had retired because he “couldn’t stand the mediocre films”, adding, with characteristic self-deprecation: “It was the secret of my lack of success.” Yet for countless film-makers, and especially for distributors of foreign and independent films, Derek was the epitome of a trusted supporter and guide.

He is survived by Sarah, and by a daughter, Jackie, from his first marriage, to Barbara Ibbott, which ended in divorce in 1966.

• Derek Elliston Michael Malcolm, film critic, born 12 May 1932; died 15 July 2023