Britain's competition regulator said there was a strong argument for tougher regulation of Google and Facebook to curb any negative consequences stemming from their domination of online advertising.
The Competition and Markets Authority (CMA) said Google accounted for more than 90% of all revenue earned for search advertising in the UK in 2018, with revenue of about 6 billion pounds, and Facebook accounted for almost half of all display advertising in the same year.
It said 'big' was not necessarily 'bad' and the platforms had brought innovative and valuable products and services to the market, but it was concerned their position may have negative consequences for the people and businesses who used their services every day.
It was also concerned that people did not feel in control of their data when they were on the platforms.
"Most of us visit social media sites and search on the internet every day, but how these firms work can be a mystery," CMA Chief Executive Andrea Coscelli said.
"Digital advertising fuels big businesses like Google and Facebook and we have been building a picture of how this complex new market works."