Showing cigarette brands on fictional TV shows is unnecessary and of questionable legality, experts said, after they found that tobacco branding is particularly common in popular soap Coronation Street.

Researchers said there should be tighter regulations on television programmes with "gratuitous depictions of tobacco" after they found that one in eight programmes show people smoking and 34% contain some form of content relating to tobacco.

The authors, from the University of Nottingham and King's College London, said smoking in films is a common cause of children's smoking experimentation.

The study, published in Tobacco Control, found 73 of the 613 programmes aired showed tobacco use and 210 contained tobacco content including people smoking, implied use of smoking, tobacco paraphernalia and tobacco brands.

Tobacco advertising, promotion or sponsorship are banned in the UK but TV shows can still show smoking imagery for artistic or editorial purposes.

The authors said: "We would recommend future television programming remove gratuitous depictions of tobacco, particularly actual smoking and tobacco branding before the 9pm watershed."

A Coronation Street spokeswoman: "We strive to balance dramatic realism with social responsibility; and ITV is careful not to condone or to glamorise smoking in any way."