An Yves Saint Laurent ad has been banned for featuring a model with a visible rib cage and knees and thighs of a similar width.

The ad, which appeared in Elle UK magazine, featured a black and white photo of a woman described by the Advertising Standards Authority (ASA) as “unhealthily underweight”, wearing a short black dress and high heels and lying on the floor with her eyes closed.

A reader complained that the ad was irresponsible for using a model who appeared to be unhealthily thin.

The ASA said YSL “indicated that they did not agree with the complainant's view that the model was unhealthily thin” but did not provide a detailed response.

Elle UK told the watchdog it had no comment to make on the complaint.

The ASA said the model’s pose and the lighting drew particular focus to her chest, where her rib cage was visible and appeared prominent, and to her legs, where her thighs and knees appeared a similar width.

It said: “We therefore considered that the model appeared unhealthily underweight in the image and concluded that the ad was irresponsible.”

It ruled that the ad must not appear again in its current form, adding: “We told the advertisers to ensure that the images in their ads were prepared responsibly.”

YSL declined to comment on the ruling.

Earlier this year, a campaign for the YSL perfume Black Opium was cleared by the ASA following complaints that it glamorised and trivialised drug use and addiction.