Adverts for Nike, Superdry and Lacoste have been banned for making misleading claims about their green credentials.

The UK’s advertising watchdog challenged the brands over the use of the word “sustainable” in paid-for Google ads which were not backed up by evidence of their sustainability.

The Advertising Standards Authority (ASA) identified three adverts from the retailers promising customers “sustainable materials”, “sustainable style” and “sustainable clothing”.

The UK’s advertising code states that the basis of claims about environmental sustainability must be clear and “supported by a high level of substantiation”.

In each case, it asked the companies for evidence to back up the claims about the sustainability of the products.

Nike said its advert, promoting tennis polo shirts with the tagline “serve and ace with Nike… sustainable materials”, was framed “in general terms” and highlighted the wider sustainability of its products.

The trainer giant said its claim about “sustainable materials” 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 customers would understand to mean its clothes were either stylish, sustainable or both.

The retailer argued it did not suggest all Superdry products were sustainable.

But the ASA said its green claims were “ambiguous and unclear” and would lead customers to believe all Superdry products were sustainable.

“Superdry had not provided evidence to demonstrate that their products had no detrimental effect on the environment,” its ruling said.

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 while there had been a reduction in the environmental impact of the 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. It has been using artificial intelligence (AI) to identify adverts which potentially fall foul of its rules.

A Nike spokesperson said: “We have engaged with the UK Advertising Standards Authority on this matter and have taken the necessary required actions. We remain committed to providing consumers with clear information to help them make the choices that are right for them.”

Superdry and Lacoste were asked to comment.