The UK's Competition and Markets Authority is investigating how Google and Facebook influence the digital advertising market.
The key concerns relate to market power, the lack of consumer control over the use of their data and the ways in which this is monetised.
"Recent studies of digital markets in the UK, US, Europe and elsewhere have raised concerns about the market power of the large platforms and whether this might be harming competition and consumers, particularly by creating barriers to new entrants," says the regulator.
"Although online platforms often provide services to users for ‘free’, in practice consumers are paying through the attention and data that they provide to the platforms, which the platforms monetise by selling digital advertising.
"As online platforms have grown, so has the revenue from digital advertising. Digital advertising to UK consumers has experienced rapid growth during the past decade, to a point where it currently comprises over 50% of UK advertising expenditure and is forecast to continue to grow strongly in the future."
In March, Google was fined €1.49 billion (AU$2.38 billion) in Europe for restricting its rivals from placing their search ads on third-party websites. The EU also last year fined Google €4.3 billion (AUD6.9 billion) for blocking competitors across its mobile Android platform.
In Australia, consumer watchdog the ACCC has presented to the federal government its final report on an investigation into Google and Facebook and their impact on media and advertising.
The inquiry looked at the impact of digital platforms on the supply of news and journalistic content and the implications of this for media content creators, advertisers and consumers.
Treasurer Josh Frydenberg has not yet released the report.
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