The scene is Adolf Hitler's bunker. The Führer stares at a map, surrounded by fearful generals. As they deliver bad news, he removes his spectacles with a trembling hand, the fury rising in him like a volcano. Speaking guttural German, his unkempt hair flopping over his forehead, Hitler explodes in a hysterical rage about Cristiano Ronaldo leaving Manchester United. Or about his crushing defeat in the Glasgow East byelection. Or about his stolen car, his Xbox Live console, or just about anything else you can imagine.

These are the improbable scenarios sweeping YouTube and other video sharing sites on the web. In clips typically lasting about four minutes, the pictures and sound are from Downfall, the hit 2004 German film about the last days of Hitler, played by Bruno Ganz. But the subtitles bear no relation to what is being said. Instead they have been rewritten, and carefully synchronised to the action, by internet jokers evidently with time on their hands. And what started as a one-off gag has now been repeated again and again over hundreds of different subjects. Downfall spoofs are now running riot over the web, lampooning politicians, footballers, even Hitler himself.

Narratives have included Hitler fulminating about Hillary Clinton's election defeat, Barack Obama's speech in Berlin, and Labour's byelection defeat by the SNP. In one, the apoplectic dictator says he would rather watch Hermann Göring pleasure himself 'than sit through another Adam Sandler comedy'. The wittiest or most topical have a habit of going viral, as users share them with friends, who pass them on in turn. Each week brings another instalment of Hitler's rants spinning into your inbox. The Downfall spoof has become the medium of choice for armchair satirists.

It is particularly popular among football fans and has been adapted endlessly to different teams. The most viewed is 'Ronaldo Leaves Utd', posted in June when rumours were rife that the Portuguese star would quit Manchester United to join Real Madrid, and now viewed nearly a million times. As Ganz, who was praised for perhaps cinema's most convincing portrayal of Hitler, speaks German in the tense atmosphere of the map room, the fake subtitles read: 'No problem, we have Ronaldo. The greatest player on planet. He will ensure we are triumphant once again. Fuck Arsenal & Chelsea.'

The Nazi officers look nervously at each other, wondering who is going to break the grim news. A sweating, nervous soldier in uniform stammers, 'Sir ... I, err ... sir ... ' Another plucks up the courage to inform the Führer: 'Ronaldo is to be sold to Real Madrid in the next few days. He has request [sic] a transfer to the biggest team in the world.' It is then that Hitler shakes with anger. Finally he says: 'Anyone who supports Arsenal, Chelsea or that scouse shit Liverpool, fuck off now... Man City fans as well, go now.' He then unleashes a manic tirade of profanities about the player who 'has dared to turn his back on the mighty REDS!!'

The scene is pivotal in the Oscar-nominated Downfall, depicting the moment when Hitler finally realises the war cannot be won. The contrast between one of history's tyrants cracking up before our eyes and talk of football transfers peppered by swear words, makes for extreme comic bathos. The harsh sound of the spoken language, the grave demeanours of the officers and the instant recognisability of Hitler all add to the effect. The more banal the subtitles, the more ridiculously hilarious the result.

The creative element of the parodies exemplifies the so-called 'Web 2.0' culture, in which internet users can make their own content and broadcast it to the world. In this case, a big budget professional movie intended for cinemas has been put in the hands of the audience who, with the help of simple video editing software, turn it into something new. Chris Hassell, director of Ralph, a London-based digital design agency which specialises in viral advertising, said: 'It's almost the perfect viral because it's easy to create and you've got a clip that can be easily adapted to anything. It's a man getting angry and it could be about anything, so it can easily be targeted at a particular group, whether it's football fans or Xbox players. It's always the same joke, but every niche interest takes it and makes it work for them. If it makes them laugh, it's probably going to work for millions of others. It's not a blank canvas, but it's the perfect basis for an idea.'

The first Downfall parody appears to have been made in Spain. Posted on YouTube by a user called 'DReaperF4' on 10 August, 2006, it shows the clip of Hitler in the map room with Spanish subtitles in which the subject is a new flight simulator game. But Chris Bowley, a student in Bristol, says he came up with the idea independently last year when he posted a clip in which Hitler sees red after being banned from playing Microsoft's Xbox Live games console. The 20-year-old recalled: 'It was very spontaneous. I was sitting in bed and the idea came to me. I had a few friends whose Xbox had been banned and I'd seen the film a few weeks before, so I thought I'd put them together.'

Bowley said that he was recently threatened with legal action over breach of copyright by Constantin Film, the production company which made Downfall. He agreed to remove the clip, which had been viewed some 2,959,881 times - making it by far the most popular Downfall pastiche of all. But he has another version, with 'slightly toned down language for younger audiences', on YouTube which has racked up nearly 80,000 views. Bowley added: 'I've made no money from the video at all, I put no ads on it. The studios don't have a case as long as the uploads aren't making a profit. It's even good advertising for them: a lot of comments on my video said, 'Where can I get the film?' Three million people have seen it.'

Among the latest spin-offs is 'Changing Giles Coren', inspired by journalist Giles Coren's irate letter to sub-editors at The Times, complaining after they removed a word from the final sentence of an article he had submitted. Asked how he felt about the spoof, in which Hitler is a chief sub-editor who learns that Coren's copy has been altered, the journalist said: 'I'm fluent in German, so watching it with subtitles is not quite as funny for me as for everybody else. There was a time when an Englishman could speak fluent French and German, but I suppose the YouTube generation spends its time doing this instead. It would be funny for me if it was in Russian.' But he went on to concede that he 'laughed a lot' at the video.

Bill Thompson, a technology expert and member of the board of the Cambridge Film Trust, said: 'We should consider the various renderings of Downfall as an art form in its own right. Just as Picasso stole from Velázquez's Las Meninas, so we should see various renderings of an original movie as a legitimate expression of creativity.'

But anyone watching Downfall might find it difficult to put the satires out of mind. 'I think the film has been broken and spoiled,' Thompson added. 'If I had made a fantastic movie like that, I would now be in despair. Bruno Ganz must weep every time he sees it.'

Other websites

Ronaldo leaves United (998, 341 views)

Hitler breaks down when he discovers Ronaldo is to sign for Real Madrid.

Barack Obama's downfall (4,448 views )

When 'media darling' Obama arrives in Berlin, Hitler is not a happy man.

Gordon Brown's downfall (42,390 views)

The scene begins as Hitler is informed they have lost the Glasgow East by-election to the SNP.

Hitler banned from playing XBox LIVE (16, 628 views)

Hitler learns that Microsoft have frozen his account.

Hitler being spied on (646 views)

Hitler learns there are videos spoofing him all over the internet.