LONDON - Google is facing a multibillion-pound legal challenge in the UK over allegations it misused its dominance in online search to inflate advertising prices and stifle competition.

A class action lawsuit seeking up to 5 billion pounds ($6.6 billion) in damages was filed at the Competition Appeal Tribunal on Tuesday. It claims that Google's practices gave it an unfair advantage by locking in its position as the default search engine on smartphones, limiting rivals' access to the market.

The case argues that by pre-installing Google Search and Chrome on Android devices through contracts with phone manufacturers, and by paying Apple to remain the default search engine on iPhones, Google undermined competition and pushed up ad prices.

The lawsuit, led by competition law specialist Or Brook on behalf of thousands of British businesses, also alleges that Google gave preferential treatment to its own advertising products by building better features and functionality into its platform.

"Regulators around the world have described Google as a monopoly and securing a spot on Google's top pages is essential for visibility," Brook said. "Google has been leveraging its dominance in the general search and search advertising market to overcharge advertisers."

Google, in response, dismissed the legal action. "This is yet another speculative and opportunistic case," a spokesperson said. "Consumers and advertisers use Google because it is helpful, not because there are no alternatives. We will argue against it vigorously."

The UK's Competition and Markets Authority (CMA) launched its own investigation into Google's search business in January, examining how its services affect advertising markets. At the time, the CMA noted that Google accounts for 90% of online searches and is used by more than 200,000 businesses in the UK for advertising.

Brook's legal team claims Google's dominance left advertisers with few options if they wanted to be visible to customers online.

The lawsuit represents the latest in a series of legal and regulatory battles Google faces in Europe and beyond over its market practices in the digital economy.