Facebook is under investigation in the UK by the competition regulator once again, this time for the social media giant's advertising practices.

The Competition and Markets Authority (CMA) said on Friday that Facebook may hold an "unfair advantage" due to its dominant market position in the digital advertising space.

Facebook might be abusing that dominance, the regulator added, saying it would look into how the company gathers data as part of its investigation.

The CMA will also scrutinise Facebook Login, a service that allows users to sign in to other websites using their Facebook credentials, to see whether it provides an unfair advantage to the company’s separate classified ads business, and its dating business.

"We intend to thoroughly investigate Facebook's use of data to assess whether its business practices are giving it an unfair advantage in the online dating and classified ad sectors," said Andrea Coscelli, chief executive of the CMA.

"Any such advantage can make it harder for competing firms to succeed, including new and smaller businesses, and may reduce customer choice,” Mr Coscelli added.

Facebook said in a statement to Reuters news agency that it would cooperate fully with the investigation.

"Marketplace and Dating offer people more choices and both products operate in a highly competitive environment with many large incumbents," the company said.

Earlier this year, the CMA launched a separate probe into Facebook after receiving complaints from "several developers reporting that Apple's terms and conditions are unfair and could break competition law".

The regulator did not reveal the identity of these developers, but the company's most powerful rival and critic in recent months - Facebook - has filed competition complaints about Apple elsewhere, as have Spotify and Fortnite-maker Epic Games.

The CMA said its investigation involved establishing "whether Apple has a dominant position in connection with the distribution of apps on Apple devices in the UK".