British regulators on Friday began searching the London offices of Cambridge Analytica (CA), the scandal-hit communications firm at the heart of the Facebook data scandal, shortly after a judge approved a search warrant.

Around 18 enforcement agents from the office of Information Commissioner Elizabeth Denham entered the company's London headquarters at around 8:00pm (2000 GMT) to execute the warrant.

The High Court granted the raid request less than an hour earlier, as Denham investigates claims that Cambridge Analytica may have illegally harvested Facebook data for political ends.

A full explanation of the legal ruling by Judge Anthony James Leonard will be issued on Tuesday, according to the court.

"We're pleased with the decision of the judge," Denham's office said on Twitter.

"This is just one part of a larger investigation into the use of personal data and analytics for political purposes," it added in a statement.

"As you will expect, we will now need to collect, assess and consider the evidence before coming to any conclusions."

The data watchdog's probe comes amid whistleblower accusations that CA, hired by Donald Trump during his primary campaign, illegally mined tens of millions of users' Facebook data and then used it to target potential voters.

Fresh allegations also emerged Friday night about the firm's involvement in the 2016 Brexit referendum campaign.

Brittany Kaiser, CA's business development director until two weeks ago, revealed it conducted data research for Leave.EU, one of the leading campaign groups, via the UK Independence Party (UKIP), according to The Guardian.

'I was lying'

Kaiser, 30, told the newspaper she felt the company's repeated public denials it ever worked on the poll misled British lawmakers and the public.

"In my opinion, I was lying," she said. "In my opinion I felt like we should say, 'this is exactly what we did.'"

CA's suspended chief executive Alexander Nix told MPs last month: "We did not work for Leave.EU. We have not undertaken any paid or unpaid work for them, OK?"

Nix was suspended this week following the Facebook revelations and a further media sting in which he boasts about entrapping politicians and secretly operating in elections around the world through shadowy front companies.

He has already been called to reappear before British lawmakers to explain "inconsistencies" in past testimony about the firm's use of the data.

Meanwhile, Facebook founder Mark Zuckerberg has been forced to issue a statement outlining his firm's role in the scandal and apologised on Wednesday to its billions of users for the breach.

The company has seen its stock market value plunge by around $75 million amid the crisis, as shares closed the week down 13 percent — their worst seven days since July 2012.

Cambridge Analytica denies any wrongdoing, and said on Friday it was undertaking an independent third-party audit to verify that it no longer holds any of the mined data.

"As anyone who is familiar with our staff and work can testify, we in no way resemble the politically-motivated and unethical company that some have sought to portray," acting CEO Alexander Tayler said in a statement.

He apologised for the firm's involvement, but said it had licensed the data from a research company, led by an academic, that "had not received consent from most respondents".

"The company (CA) believed that the data had been obtained in line with Facebook's terms of service and data protection laws," Tayler said.

New review

Aleksandr Kogan, a University of Cambridge psychologist, created a personality prediction app that harvested the data of 270,000 people who downloaded it — as well as scooping up the information of their friends.

That was possible under Facebook's rules at the time, and Kogan this week claimed he was being unfairly blamed.

"I'm being basically used as a scapegoat by both Facebook and Cambridge Analytica," he said in interviews on Wednesday.

"We were assured by Cambridge Analytica that everything was perfectly legal and within the terms of service" of Facebook, he added.

However, Cambridge University announced on Friday it was "undertaking a wide-ranging review" of the episode and had written to Facebook "to request all relevant evidence in their possession".

"Should anything emerge from this review, or from our request to Facebook, the University will take any action necessary in accordance with our policies and procedures," it said in a statement.