The Competition and Markets Authority (CMA) said its provisional findings showed Google was using anti-competitive practices in the ad tech stack – a set of services which facilitate the sale of online advertising space between sellers and buyers.

The CMA has previously said Google has a strong position at various different levels of this space, providing a wide range of services including platforms where advertisers can buy online advertising space, as well as technology that automates the sale of advertising space and managing ad inventories for publishers.

The regulator’s provisional investigation has now found that when placing digital ads on websites, the vast majority of publishers and advertisers use Google’s ad tech services.

The CMA said it was concerned Google was actively using its dominance in the sector to give preference to its own services.

Juliette Enser, interim executive director of enforcement at the CMA, said: “We’ve provisionally found that Google is using its market power to hinder competition when it comes to the ads people see on websites.

“Many businesses are able to keep their digital content free or cheaper by using online advertising to generate revenue. Adverts on these websites and apps reach millions of people across the UK – assisting the buying and selling of goods and services.

“That’s why it’s so important that publishers and advertisers – who enable this free content – can benefit from effective competition and get a fair deal when buying or selling digital advertising space.”

In response, Google’s vice president of global ads, Dan Taylor, said: “Our advertising technology tools help websites and apps fund their content, and enable businesses of all sizes to effectively reach new customers.

“Google remains committed to creating value for our publisher and advertiser partners in this highly competitive sector.

“The core of this case rests on flawed interpretations of the ad tech sector. We disagree with the CMAs view and we will respond accordingly.”

The CMA said it had issued a statement of objections to Google on the issue, and would now carefully consider representations from the tech giant before reaching a final decision.