Some lauded them as plucky local heroes who harnessed new technologies to tackle problems that the authorities ignored. Others saw them as snoops with no regard for people's privacy.

Exasperated Madrid residents who filmed prostitutes negotiating with their clients outside their homes and broadcast them on YouTube have been fined for infringing the Spanish data protection Act.

In recent years city hall in Madrid has spent hundreds of millions of euros beautifying the area around Puerta del Sol, one of the principal meeting points for tourists in the city.

Even after its facelift, Calle de la Montera has remained a haven for prostitutes from Eastern Europe and Africa, who ply their trade yards from a police station on the street.

Tired of official indifference, residents took matters into their hands last year by installing webcams and recording images of the prostitutes' clients.

Twenty-two of them were then placed on the YouTube website in the hope that they would act as a deterrent for the men if there was the danger that their wives would spot them attempting to buy sex.

The Spanish Data Protection Agency, however, has ordered the neighbours to take down the webcams and fined them 601 euros (£475) for broadcasting images of passers-by without their consent.

The government-funded body said it was the first time that it had taken action against private citizens for invading people's privacy.

It gave warning that it was looking into several other cases in which people had become the unwitting stars of internet videos. “The investigation has concluded that there was a grave infraction of the data protection law,” the agency said, although it cited the desire of the neighbours to tackle crime and periodic efforts to obscure people's faces as mitigating factors.

Residents were angered by the fine. “I don't think it's reasonable to fine people for filming their faces,” Gilmar Barbosa, vice-president of a local neighbourhood association, said. “Residents have been suffering harassment for years, with noise, crime and rubbish.”

Ana, a resident of the street, was quoted by Spanish media last year as saying that they were driven to use the webcams after the number of prostitutes on the street increased dramatically.

“Only the nationality of the young women has changed,” she said. “For a time, they were Latin American and now they are mainly from Eastern Europe.”

Prostitution is widely tolerated in Spain and is not, in itself, illegal. The country's most respected national newspapers are packed with graphic adverts for prostitutes.

Roadside brothels with flashing neon signs adorn the big highways and most cities have neighbourhood sex clubs. Police estimate that there are at least 1,000 such brothels operating openly in Spain.

They are certainly not short of clients. A recent survey by the Carlos III Institute found that 25 per cent of Spanish men between the ages of 18 and 49 said that they had visited a prostitute, compared with 1.3 per cent of British men.

The residents of Calle de la Montera may have lost their battle to push the prostitutes elsewhere but they have achieved something: city hall has installed its own cameras on the street, which are monitored by police and can be used as evidence in a trial.

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