Tough chaps: Robert Donat Season at BFI

They were movie heroes – but nothing like today's action men. Ahead of a season of classic films, Geoffrey Macnab salutes the 'bulldog breed'

He will generally be wearing a tweed jacket and flannel trousers. Often, he will smoke a pipe. He might have a moustache or slicked-back hair, but there will be nothing too extravagant about his appearance. Put him in the most extreme situations and he will still keep his manners. He is well-spoken, self-reliant and always chivalrous. He has a dry sense of humour. Welcome to the world of the "gentleman amateur", the hero of countless British films of the middle part of the last century.

Robert Donat, who died 50 years ago, was one of the supreme examples of the type. In Alfred Hitchcock's The 39 Steps (1935), as John Buchan's Richard Hannay, Donat takes unflappability to a new high. Whether dangling from the Forth Rail Bridge, handcuffed to Madeleine Carroll, mistaken for a politician and forced to give an impromptu speech, or pretending he is a milkman, Donat never loses his poise. At the same time, he manages to convey both idealism and self-deprecating humour.

In Jacques Feyder's Knight Without Armour (1937), that trademark insouciance and imperturbability is again in evidence. Donat plays a British secret agent in revolutionary Russia. Not only is he cast opposite one of cinema's most notorious scene-stealing femme fatales in Marlene Dietrich, and pitched into a world of mad Bolsheviks and White Russians, Feyder also obliges him to wear some unflattering furry headgear. His poise is never threatened for an instant.

Donat had a vulnerability about him (perhaps a consequence of the chronic asthma that blighted his life and career) that made audiences warm to him all the more. In The Age of the Dream Palace, his classic book about British cinema of the 1930s, Jeffrey Richards brackets Donat with Leslie Howard as British cinema's most important "romantic adventurers". Both, Richards notes, were seen as "quintessentially English" despite having eastern European fathers. They were often offered the same roles.

There was often a forlorn quality to both men. They epitomised a kind of heroic defeatism – a noble, chivalric failure that appealed to a nation that considered Captain Scott of the Antarctic as a prime hero and still liked to celebrate the charge of the Light Brigade. They had a gentleness about them, too, that you simply didn't find in Hollywood heroes of the era. You couldn't, for example, ever imagine Clark Gable playing a fop like Howard's Sir Percy Blakeney in The Scarlet Pimpernel (1934), or Spencer Tracy as a doddering old school teacher in a film like Goodbye, Mr Chips (1939).

Howard could even play a clubfooted cuckold, as he did opposite Bette Davis in Of Human Bondage (1934), without forfeiting an audience's sympathy. Donat and Howard may have been on the effete side, but both actors had immense followings among female fans. As Jeffrey Richards wrote of them, they "epitomised romantic as opposed to sexual love, the pure, decorous, yearning sort of love that characterised the ideal of courtly chivalry, a love of what Graham Greene called 'discarnate embraces'."

During the Second World War, both men (Howard in particular) stood for tolerance and courage. In Powell and Pressburger's propaganda picture 49th Parallel (1941), Howard's eccentric Englishman is deliberately contrasted with the gimlet-eyed Nazis. "His courage and gentle humour went along with the message that England was fighting to save civilisation, high culture, intellect," Angus Calder writes of Howard in his study The Myth of the Blitz (1991). Howard's strange death – shot down on his return to London from a secret mission to Lisbon, by Nazis convinced that Churchill was aboard his plane – added to his mythical quality. Donat and Howard spawned numerous lesser imitators. In their wake, the "gentleman amateurs" they had played with such wit and humour slowly metamorphosed into the "chap" – the repressed and often boorish type who passed for a leading man in too many British films of the 1940s and 1950s.

It is dispiriting to compare post-war British cinema with its American equivalent. In the US, this was the beginning of the "method" era, of the teen movie and of rock'n'roll. Stars like John Garfield, Montgomery Clift, Marlon Brando and James Dean appeared on screen playing sensitive and rebellious anti-heroes. Meanwhile, back in Britain, the likes of Kenneth More and Jack Hawkins came into their own. They didn't play poetry-loving aesthetes as Donat and Howard had. They dressed like geography teachers and had a brisk, no-nonsense demeanour. They may have been "good eggs", but you get little sense of thought or emotional depth in their performances..

The "chaps" – who in the post-war years included such actors as Dirk Bogarde at the start of his career in the "Doctor" films, John Gregson and More in Genevieve, and Ian Carmichael in various Boulting brothers farces – had completely lost the idealism and sense of yearning that Donat and Howard always had. They were hearty, lecherous, sometimes comically inept, sometimes heroic in deadpan fashion, but their performances were straight from seaside rep.

Arguably, Donat and Howard's real successors were the "boffins" played by actors like David Farrar and Michael Redgrave in films like The Small Back Room (1949) and The Dam Busters (1955). Redgrave, who often gave the appearance that he was only appearing on the screen under sufferance and would far rather have been performing "proper" plays at The Old Vic, had played a Robert Donat-like gentleman-amateur early in his career in Hitchcock's The Lady Vanishes (1938). He pulled his role off with elan, showing heroism, self-mocking irony and treating Margaret Lockwood with an unexpected gallantry. However, his greatest screen roles were as tormented, introspective men who may have professional expertise but seem incapable of dealing with real life.

In The Dam Busters, he plays the inventor Barnes Wallis as a nervous, stooped figure in a mackintosh, whose methods and demeanour are so odd that he struggles to get anybody to take him seriously. He was even better as Crocker-Harris, the cuckolded and self-loathing classics teacher at a minor public school in The Browning Version (1951). David Farrar, meanwhile, enjoyed his finest moment as the alcoholic bomb disposal expert in The Small Back Room. He may have delirium tremens and be prey to hallucinations and sexual anxiety but it doesn't stop him from defusing the German booby trap.

The "chaps" and the "gentleman amateurs" were largely swept away in the New Wave era of the late 1950s and early 1960s when actors like Sean Connery, Albert Finney, Peter O'Toole, Richard Burton and Richard Harris emerged.

They haven't disappeared entirely. Hugh Grant in Notting Hill isn't so different from the hapless Englishmen played by the likes of Bogarde and Ian Carmichael in the 1950s. But you don't see many in the current crop of British horror and gangster movies. More regretfully, the Brits have also failed to discover many new actors with the flair of Robert Donat or Leslie Howard – actors who could convey sensitivity and yearning as well as humour and heroism.

'The 39 Steps' is re-released on 11 April as part of a season of Robert Donat's films at BFI Southbank