A new UK watchdog is to police the dominance of tech giants such as Google and Facebook to try to prevent them exploiting consumers and small businesses.
The Digital Markets Unit will enforce a new code of conduct governing the behaviour of the powerful online platforms.
The move comes in response to government concerns that the corporations are restricting growth of the sector and hampering innovation.
Image:Alok Sharma has raised concerns over the dominance of just a few big tech firms
The new body, which will lie within the Competition and Markets Authority (CMA) and co-ordinate with regulators including Ofcom and the Information Commissioner's Office, is due to begin work in April.
It could be given powers to suspend, block and reverse decisions made by technology firms and to impose fines for failing to follow the rules.
Companies will have to be more transparent about how they use consumer data and restrictions that make it hard to use rival platforms will be banned, the government said.
The rules also aim to support the news industry by rebalancing the relationship between publishers and platforms.
Business Secretary Alok Sharma said: "Digital platforms like Google and Facebook make a significant contribution to our economy and play a massive role in our day-to-day lives - whether it's helping us stay in touch with our loved ones, share creative content or access the latest news.
"But the dominance of just a few big tech companies is leading to less innovation, higher advertising prices and less choice and control for consumers.
"Our new, pro-competition regime for digital markets will ensure consumers have choice, and mean smaller firms aren't pushed out."
Google and Facebook dominate digital advertising, accounting for around 80% of the £14bn spent in 2019, according to the CMA.
The two US companies have said they are committed to working with the UK government and the regulator, including giving users greater control over their data and the ads they receive.
The crackdown forms part of a wider push by governments in the US and Europe to curb the power of big tech firms in the face of concerns about their influence.
The European Union has unveiled proposals to take control of data from companies and is set to release details next month of a shake-up of digital regulations aimed at preventing competition being stifled.
In the US, the authorities are pursuing an antitrust case against Google, and politicians have proposed breaking up large tech companies.