His gamble paid off: the producers were so encouraged by what he showed them that they allowed Blackmail to be reshot with sound. It was Britain's first all-talking film. Despite the addition of sound and dialogue, Hitchcock retained the silent film's freedom of movement and avoided the danger of making 'photographs of people talking'. It, too, had a show-piece scene which attracted particular attention. The heroine has, half-accidentally, stabbed a would-be seducer to death and returned home just in time to cover her absence. At breakfast the next morning a neighbour chatters about the murder - now reported in the papers: 'What a terrible way to kill a man. With a Knife in his back. A knife is a terrible thing. A knife is so messy and dreadful...' The words run together so as to be almost indistinguishable, except for the word 'knife' stabbing out of its context again and again, as though audibly striking the guilt-ridden girl.

The effect is there to be noticed, and noticeable it is, perhaps at the expense of the rest of the film, since it is rather showy and self-conscious. Nevertheless, at the time it demonstrated to producers, the public and especially the unwilling critics - who looked askance at the new talkie medium - that sound, and even dialogue, could be used creatively. The talkie did not have to be merely a photographed stage play but had other, more exciting possibilities. Blackmail confirmed Hitchcock as the most important and talented British film-maker of the day.

In 1934, he began the great series of six suspense thrillers, made in four years, which carried his reputation round the world and finally took him to Hollywood in 1939. The first of them, The Man Who Knew Too Much, established his penchant for the brilliantly conceived effect as the basis f film-making. A family on holiday in St Moritz witness the murder of a secret agent who, before he dies, tells them of a plan to assassinate a foreign diplomat in London. Realizing this, the enemy spies kidnap the couple's daughter to ensure their silence. The couple have to thwart the villians' plans without police help.

Whereas in The Lodger and Blackmail the tricks had tended to stand out from the overall texture, The Man Who Knew Too Much was virtually a succession of memorable scenes and incidents which kept the audience totally at the director's mercy. This became Hitchcock's hallmark during the Thirties and remained an important part of his style throughout his career..

Not everyone approved - Graham Greene, then influential film critic of the Spectator, wrote of The Secret Agent (1936):

'His films consist of a series of small "amusing" melodramatic situations: the murderer's button dropped on the baccarat board; the strangled organist's hands prolonging the notes in the empty church; the fugitives hiding in the bell-tower when the bell begings to swing. Very perfunctorily he builds up to these tricky situations (paying no attention on the way to inconsistencies, loose ends, psychological absurdities) and then drops them: they mean nothing: they lead to nothing.'

It was curious that Greene, of all people, should have been quite so unsympathetic to what Hitchcock was doing in these films, since it was so close to those stories of his own that he labelled 'entertainments'. Hitchcock was always first and foremost a popular entertainer, with no overt pretensions, leaving others to find deeper meanings in his work. His way of involving his audience was to deploy his unique technical skills and extraordinary inventive faculties in the elaboration of telling incident through specific effect. There are many single shots in the British thrillers which everyone who has seen them remembers. There is, for instance, the famous shot near the end of Young and Innocent (1937) in which the camera travels slowly across a crowded ballroom during a the dansant, moving closer and closer to the black-face band, then concentrating on the drummer and finally pausing in an arresting close-up of his eyes twitching - the crucial identifying mark of the murderer.