British regulators are investigating revelations that Facebook treated hordes of its users like laboratory rats in an experiment probing into their emotions.

The Information Commissioner’s Office says it wants to learn more about the circumstances underlying a 2-year-old study carried out by two US universities and the world’s largest social network.

The inquiry is being coordinated with authorities in Ireland, where Facebook has headquarters for its European operations, as well as with French regulators.

Scientists were trying to collect evidence to prove their thesis that people’s moods could spread like an “emotional contagion”

This is just the latest in a string of incidents that have raised questions about whether the privacy rights of Facebook’s nearly 1.3 billion users are being trampled by the company’s drive to dissect data and promote behaviour that could help sell more online advertising.

In this case, Facebook allowed researchers to manipulate the content that appeared in the main section, or “news feed,” of about 700,000 randomly selected users during a single week in January 2012. The data-scientists were trying to collect evidence to prove their thesis that people’s moods could spread like an “emotional contagion” depending on the tenor of the content that they were reading.

The study concluded that people were more likely to post negative updates about their lives after the volume of positive information appearing in their Facebook feeds had been purposefully reduced by the researchers. The opposite reaction occurred when the number of negative posts appeared in people’s news feeds.

Facebook has apologised and certainly we never want to do anything that upsets users

None of the participants in the Facebook experiments were explicitly asked for their permission, though the social network’s terms of use appears to allow for the company to manipulate what appears in users’ news feeds however it sees fits.

Facebook’s data-use policy says the Menlo Park, California, company can deploy user information for “internal operations, including troubleshooting, data analysis, testing, research and service improvement.”

The reaction to the study itself provided evidence of how quickly an emotional contagion can spread online. The research was released a month ago, but it didn’t provoke a backlash until the past few days after other social media sites and essays in The New York Times and The Atlantic raised red flags about the ethics of Facebook’s experiment.

As it has done in several past breaches of privacy etiquette, Facebook is now trying to make amends.

Sheryl Sandberg, Facebook’s chief operating officer, told television network NDTV in India that “we clearly communicated really badly about this and that we really regret.” Later she added: “Facebook has apologised and certainly we never want to do anything that upsets users.”

The words of contrition sounded hollow to Jeff Chester, executive director of the Center for Digital Democracy, a privacy-rights group. He points to Facebook job openings looking for researchers specialising in data mining and analysis as evidence that the company still has every intention of digging deeper into its users’ psyches and preferences.

“They are engaged in secret surveillance of its users to figure out how to make more money for their advertisers,” Chester said.

Whatever Facebook has been doing has been paying off for the company and its shareholders. Facebook’s revenue last year rose 55 per cent to $US7.9 billion ($A8.55 billion) and its stock has nearly tripled in value during the past year.