Children are being exposed to millions of images of tobacco every week on prime time television, UK scientists have claimed.

While their study focused on free to air channels in the UK, all of these channels are widely available and viewed in Ireland.

According to the scientists from the University of Nottingham, tobacco-related content already features frequently in films aimed at children and this is known to initiate an interest in smoking among them.

The scientists believe that a reduction in the use of tobacco images on television could reduce the number of young people who start smoking.

As part of their study, they analysed the content of five free to air channels in the UK. They looked at any content that was broadcast between 6pm and 10pm on three different occasions, four weeks apart in 2010.

The tobacco-related content was studied in one-minute intervals and it included the use of actual tobacco products, the implied use of products, the presence of associated items, such as ashtrays, and any other references made to tobacco.

Any tobacco branding or merchandising was also taken into account.

Altogether, 420 hours of television were analysed and this included over 600 programmes and over 1,100 advertisements and trailers. The most common types of programme shown were documentaries, news programmes and soap operas.

The study found that among the programmes shown, at least one in three included some tobacco content. This content occurred at least once in almost seven in 10 reality shows, in just over half of comedy programmes and in almost half of soap operas and dramas.

At least two-thirds of the tobacco content occurred before the 9pm watershed.

The scientists said that based on the programme content and audience viewing figures, young people were being exposed to 59 million instances of tobacco-related imagery every week, 16 million of which involved actual tobacco use.

The scientists pointed out that while the advertising and promotion of tobacco products are banned on UK television, images that are included for editorial or artistic reasons are not banned.

"We would recommend that future television programming remove gratuitous depictions of tobacco, particularly actual smoking and tobacco branding, from programmes aimed at young people or scheduled before the 9pm watershed," the team said.

Details of these findings are published in the journal, Tobacco Control.