When plot lines contain plugs for brand name products, or when logos are prominently visible on screen, chances are this is the form of stealth advertising known as product placement.

It is a practice estimated to gain more than $1 billion (€1.1 billion) in revenue for Hollywood studios trying to raise finance for high-budget pictures, while for large corporations gaining exposure alongside screen heroes and heroines is a valuable and repeatedly used marketing tool.

A potentially "dubious and dangerous practice" is how Mr Rod Stoneman, chief executive of Bord Scannβn na h╔ireann describes the technique.

"Of course, producers sometimes have to find finance every way they can but we would be wary of the consequences of product placement," he says. "Have you seen Castaway? How much of that was paid for by FedEx?"

As well as desert island film Castaway, where washed-ashore FedEx packages help a FedEx employee played by Tom Hanks to survive, the international delivery service brand name has recently starred in Runaway Bride, Bowfinger and William Shakespeare's Romeo and Juliet. One of its competitors, UPS, pops up in the Lara Croft film Tomb Raider, alongside Sony and Ericsson, while Nokia phones are used prominently in Charlie's Angels and The Matrix.

Although production companies may not receive cash payments for the "ad", they may be offered promotional support: In 1997, Ericsson spent $25 million on a tie-in campaign with the Bond film Tomorrow Never Dies, running across 57 countries.

Product placement is as old as Hollywood itself, but since sales of US confectionary Reese's Pieces shot up by 65 per cent when it was used to entice the cute alien out of the wardrobe in E.T., large corporations have increasingly seized upon product placement opportunities. Anheuser-Busch and Coca-Cola, for example, both have inhouse divisions devoted to getting a little screen time.

But while product placement on the big screen may be viewed by some producers and directors as tacky commercialism getting in the way of artistic craft, it is perfectly legal. On the small screen, the rules change. Product placement is defined as the display of brands by programme makers in exchange for payment and it is "strictly forbidden", according to the Broadcasting Commission of Ireland's (BCI) regulatory code.

Brand names are still allowed to appear on screen, the code says, "as it is not always possible in the interests of authenticity to avoid references to the names of commercial products or services in their incidental portrayal in radio and television programmes". Examples of this would include the chocolate bars in Coronation Street's corner shops or the billboards surrounding the Albert Square market.

"It is impossible to do something like a soap opera and keep it credible without having ordinary brand names on display," says Mr Niall Matthews, producer of RT╔'s Fair City. "You can't have an Irish pub without Guinness on sale. We would stock the shop and stock the pub with credible brands, because if we didn't we would have to make them up ourselves."

Mr Ciarβn Kissane, broadcasting manager at the BCI, says the body has yet to receive any complaints about undue prominence for branded goods on Irish television. "We only regulate TV3 but we haven't encountered any problems in relation to product placement. Our experience is that it doesn't happen here, but then there are not too many home-produced programmes on TV3."

In Britain, the regulations on product placement in broadcasting are similar, with Independent Television Commission codes banning the inclusion of a product or service in return for payment to the programme maker.

Advertisers are concerned by the development of TiVo black boxes, which automatically record programmes without ad breaks or allow viewers to watch the programme ad-free a few minutes after it goes to air. But if new technology is creating a drive for more plugs within programmes, it is also allowing for more easily manipulated product placement.

In the US, product placement is not allowed during fictional programmes when they are first broadcast on network television but becomes legal when the same programmes are repeated under syndication deals with cable channels. This has prompted programme makers to digitally add products to scenes at a later date: The first television show to do so was a drama called Seven Days, which in 1999 digitally added a Coca-Cola can onto a desk and a billboard advertising Wells Fargo bank.

In the Republic, these practices seem a long way off. Apart from broadcasting regulations, the self-regulated advertising industry's code states that an advertisement should be "designed and presented in such a way that it is immediately apparent that it is an advertisement".