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LONDON — The U.K.’s information and data privacy regulator is investigating whether Facebook responded “robustly” to reports that political data firm Cambridge Analytica gained access to data on 50 million of its users.

“We are looking at whether or not Facebook secured and safeguarded personal information on the platform and whether when they found out about the loss of the data, whether they acted robustly and whether or not people were informed,” Information Commissioner Elizabeth Denham told the BBC on Tuesday morning.

The offices of Cambridge Analytica in central London Henry Nicholls / Reuters

Denham first demanded access to the data held by Cambridge Analytica on March 7, the Information Commissioner's Office said in a statement. The company didn't respond by the deadline given and on Monday evening Denham announced that the ICO is seeking a warrant for the information. She did not say when regulators had started looking into Facebook.

Later on Tuesday, Cambridge Analytica said in a statement that it has offered to share the information requested by the regulator, and that it will open its offices to officials — subject to an agreement on the scope of the inspection.

Facebook had started its own audit at Cambridge Analytica's London office, but halted it at the request of the regulator, the company said Monday. The ICO said that Facebook's search "would potentially compromise a regulatory investigation."

Related: Facebook suspends Cambridge Analytica, which worked for Trump campaign

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On Saturday, the New York Times and London's Observer reported that the firm harvested private information from more than 50 million Facebook users to influence voters during the 2016 election.

“We are looking at whether or not there was sufficient consent for individuals to be able to share their data with the application in the first place,” Denham said.

The probes of the two companies are part of a larger investigation by the regulator into the use of personal data in political campaigns, Denham said.

The British government has called the allegations “very concerning.”

"It is essential that people can have confidence that their personal data will be protected and used in an appropriate way," a spokesman for Prime Minister Theresa May said on Monday.

On Tuesday, a senior British lawmaker requested that Facebook Chief Executive Mark Zuckerberg appear before Parliament's media committee in relation to the reports.

"It is now time to hear from a senior Facebook executive with the sufficient authority to give an accurate account of this catastrophic failure of process," Damian Collins, the chairman of the Digital, Culture, Media and Sport Committee, said in a letter addressed to Zuckerberg. "I hope this representative will be you."

Collins earlier alleged that Cambridge Analytica Chief Executive Alexander Nix had "deliberately misled" his committee during testimony about its use of Facebook data.

It's time for Mr. Zuckerberg and the other CEOs to testify before Congress. The American people deserve answers about social media manipulation in the 2016 election. — Mark Warner (@MarkWarner) March 20, 2018

In the U.S., both Democrats and Republicans issued strong statements calling on Facebook to make changes and questioning whether the company had grown too big, too fast.

Sen. Mark Warner, the vice chairman of the Senate Intelligence Committee, tweeted on Tuesday that it was "time for Mr. Zuckerberg and the other CEOs to testify before Congress."

On Monday, NBC News’ U.K. partner ITN Channel 4 News broadcast a meeting captured on hidden camera between the head of Cambridge Analytica and their reporters posing as potential clients interested in changing the outcome of the Sri Lankan elections.

The reporters, who were trying to find out how the company operated, learned about the novel and deceptive methods employed by the company, including bribes, blackmail, and misinformation campaigns.

They recorded Alexander Nix, chief executive of Cambridge Analytica, discussing the idea of hypothetically entrapping an opposition leader. He described how the company could record a person accepting a bribe, "an offer he can't refuse" or "send some girls around to the candidate’s house."