The Advertising Standards Authority (ASA), the U.K.'s advertising watchdog, has challenged Nike, Superdry and Lacoste over the use of the word "sustainable" in paid-for Google ads that were not backed up by evidence of their sustainability, according to BBC News.

The ASA has identified three adverts from the retailers that promise customers "sustainable materials," "sustainable style" and "sustainable clothing," claims that the U.K.'s advertising code states must be clear and "supported by a high level of substantiation."

In each case, it has asked the companies for evidence to back up the claims about the sustainability of the products. Standards for advertising are much stricter in the U.K. and Europe than in the U.S., where claims of being the “biggest” or “best value,” as well as “sustainable,” are not subjected to requirements of objective proof.

Nike said its advert, promoting tennis polo shirts with the tagline "serve and ace with Nike… sustainable materials," referred to "general terms" and was intended to highlight that other products available on its site incorporated recycled materials.

But the ASA ruled Nike had failed to include qualifying details, and had not explained the basis of its claim about the "sustainability" of its products.

Superdry's advert promoted a "wardrobe that combines style and sustainability," which it argued did not suggest all Superdry products were sustainable, but that customers would infer that its clothes were either stylish, sustainable or both.

But the ASA said in a ruling that Superdry had “not provided evidence to demonstrate that their products had no detrimental effect on the environment."

Lacoste's advert promoted its kids' range as "sustainable clothing," and told the ASA it had worked for years to reduce the carbon footprint of its products.

But the watchdog said that, although the clothing brand had achieved a reduction in the environmental impact of products in its kids' range, it had not offered evidence that its clothing would have "no detrimental effect on the environment."

In each case, the adverts were banned and the companies were warned future promotions must contain "a high level of substantiation" for any sustainability claims.

The three rulings form part of a wider crackdown by the ASA on brands making misleading green claims in adverts, also known as greenwashing. The BBC reports that the ASA has been using artificial intelligence to identify adverts that potentially fall foul of its rules.

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