Television coverage of some international sporting events will in the future come with a "brand warning". Around the time the opening credits are flashed up on screen a line will appear advising viewers that "brands have been electronically changed". It is one of the European Association of Advertising Agencies' responses to the growing phenomenon of virtual advertising, whereby, for example, pitch-side posters can be electronically changed to show different brands in different countries.

The implications of the practice first hit home to the association during a Spanish cycle race. It was sponsored by Heineken and most European viewers would have seen cyclists crossing the line in front of Heineken branding. However, viewers in Spain and Greece would have seen the same cyclist crossing the same line in front of a poster for Amstel, also produced by Heineken. It had been changed electronically by the sponsor because that is its strongest brand in those countries.

"This sort of virtual advertising is happening more and more, especially in America but increasingly in Europe," says Mr Stig Carlson, director general of the association. "What's important to us is that viewers know that the image they are seeing has been modified, hence on-screen warnings."

Devising EU-wide advertising agency initiatives is part of the association's brief and it covers all media. "At present, differing advertising restrictions in individual countries mean that there cannot be complete communication across Europe," says Mr Carlson, "and clearly this does not reflect the EU's objective of free movement of goods and services."

The list of differences in terms of advertising rules and regulations between countries is endless. Finland, for example has recently re-permitted alcohol advertising on television after a 50-year ban, while its nearest neighbour, Sweden, is fervently committed to maintaining a total ban.

Differing restrictions when it comes to alcohol and tobacco are perhaps predictable but most countries have their own idiosyncratic rules for a whole range of products. In France newspapers and books cannot be advertised on television; in Greece, toy advertising is banned until after 11 p.m.; only state lotteries are allowed to advertise on TV in Nordic countries; and price promotion is prohibited in Germany.

As the EU is committed to advertising harmonisation, such differences will have to be ironed out in the coming years through self-regulation within the industry and direct EU legislation.

Mr Carlson was in Dublin yesterday to give a seminar to advertisers and agencies on the association's various papers. He was also keen to get information from his audience, especially about car advertising. "One of the ways we advise Brussels on advertising legislation," he says, "is by knowing what works and doesn't work in different countries."

According to Mr Carlson, Britain is currently lobbying for a restriction on the volume of car advertising, arguing that it will cut down on road accidents. His agency intends to fight this. "Our argument is that car advertising can be socially responsible in terms of anti-speeding messages and so on," he says. "Ireland has always been strong on that, so I am collecting examples that will back up our argument."