US tech groups already face fierce scrutiny of their impact on society, from politicians and consumer advocates, activist investors and their own former employees. Now some of their biggest customers are stepping up criticism of a digital ad market dominated by Google and Facebook. Unilever, one of the world’s largest marketing spenders, is threatening to pull its ads from digital platforms if they “create division”, foster hate or fail to protect children.

It is not the first time Keith Weed, Unilever’s chief marketing officer, has criticised what he calls the “murky” world of digital media. In the past, he focused on the tech platforms’ lack of transparency over data and metrics, pressing them to make sure ads were being viewed by real people. The crucial issue now, he argues, is whether consumers trust what they see online, given concerns about fake news, election meddling, trolling and the platforms’ failures to police content that glorifies terrorism or exploits children.

These are generally seen as ethical issues demanding a response in the form of regulation, such as Germany’s introduction of fines for companies that fail to remove hate speech or fake news. But from the advertisers’ point of view, it is a matter of quality control: the digital platforms promise that ads will appear next to appropriate content, and they have proved unable to ensure that this is always the case.